Far too many things can go horribly wrong when one decides to make his or her own computer. Most of these problems are minor and involve losing screws or having a broken floppy drive, but some are considerably nastier. Now, I'm not saying this happens to everyone: only the incompetent and the unlucky, both of which I am. Despite this, however, I've only had a few of these happen to me; the rest are from others' experiences. Remember, with the exception of all but the fourth one on this list, this is what CAN happen, not what will.

The motherboard will rub against the case, make constant contact with the power supply, fall onto a rug, or just make too much contact with your hand.





The power supply will fall off and land on your video card. (*)





If the video card has a particularly heavy heatsink on it and the above happens, the power supply will probably knock it off and fall onto whatever's below, like your modem, NIC, and/or sound card.





Applicable to sockets that rely on clip heatsinks only (Socket 370/A, Super Socket 7, etc.): The CPU heatsink will take five hours to get on, because its clip mechanism was designed by Satan. (This is true for all clip-based CPU heatsinks.) Getting it on will require the use of an absurdly small screwdriver, a considerable amount of brute force, and luck. The screwdriver will slip and smash into your motherboard at least twice. No actual damage of any kind will occur, except maybe to your blood pressure.





If the any of the video card's heatsinks are secured with frag tape, they will promptly fall off and land on the modem/NIC/sound card below.





You will lose at least half of the screws needed to fully assemble the computer.





You put a Celeron in it.





If you have your screws sorted out in a little tray, you will be unable to locate two of them. One of them will be under the computer, and the other will be on your person. The latter will only be found when you get up and do a tap-dance.





When you turn the computer on, you will suddenly discover that at least one cable is a little too near a case fan. The most likely outcome (a loud scraping noise that will alert you to the problem immediately) is also the least harmful, which is why it will not happen to you. Instead, the fan will quietly get stuck on the cable and kill its motor. Alternatively, one of the fan's blades may snap off, which is louder and funnier but just as unfortunate.





If you have a heavy (450g+) CPU heatsink on a Socket A or Socket 370 motherboard, it will eagerly demonstrate certain basic laws of physics when the computer is moved around and land on the video card, taking the motherboard's plastic socket clip with it.





Every single cable in the entire computer will thwart your attempts to insert the RAM.





When you finally fight back the cables, you will spend approximately fourteen minutes lining up the RAM perfectly with the slot. When you push to get it to go in, it will fall out, and the cables will gleefully return to their former nesting place.





The CD-ROM drive at the top slot will make increasingly worrying noises when turned on. The more you worry about it, the less likely the possibility that it is a serious problem becomes.





The computer will fail to POST when turned on, and will make several loud beeps. If you find a guide to beep codes for your particular BIOS, that particular beep code will turn out not to exist. That does not, of course, stop your BIOS from making it.





You will find that you have bought a 24-pin ATX power supply and a 20-pin ATX motherboard. There are adapters for this, but they are hideous, likely to break, and very clumsy.





You will find that you have bought a 20-pin ATX power supply and a 24-pin ATX motherboard. There are adapters for this, but in addition to being hideous, likely to break, and very clumsy, they do not work.





Applicable to PATA: You will find two PATA cable sockets, which will be different colors. Your PATA cables' plugs will be different colors at both ends, and often the color of one plug will match with the first ATA cable socket and the color of the other plug will match with the second ATA cable socket.**





Applicable to PATA: Your motherboard will deny the existence of an ATA cable in the second plug while booting the devices attached to that cable without trouble. This is unrelated to the colors of the cable plugs, but changing the plugs around will cause the error message to change slightly while simultaneously convincing your BIOS that you have four ATAPI CD-ROM devices.





The rear case fan will come loose, and the vibration it creates will cause it to fall-- that's right-- onto the video card, probably making a mess out of some cables on the way.





If you've made the mistake of working on the computer next to the desk it will be on or under, the keyboard and mouse will fall on your head when you're trying to get one of the parts into a slot or socket.





If you have a Micro ATX case, you are probably doomed to spend about thirty minutes just screwing in a single goddamned CD drive.





You will mix up the PWRON/STRLED/etc. plugs, due to that the writing on the motherboard as to which part of the big copper plug goes to which plug is all absurdly small and misaligned with where the plug should actually go.





Once everything is operational and the computer POSTs, you will realize that the CD containing the operating system is scratched. Badly.





Once the operating system and all needed software is installed and fully configured, the hard drive will make loud grinding noises and cease operation, necessitating its exchange for a new hard drive that will do exactly the same thing.

* This happened once when I had finished screwing the PSU in in a cheap midi-tower. I had made the stupid mistake of using slightly smaller but otherwise identical screws to screw it in, and when I shoved the tower back, wham. Amazingly, the video card (a Chaintech GeForce3 Ti200) was unharmed.

** In theory, the color-coding for PATA cables is supposed to be simple: blue is the plug that you stick into the motherboard, black is the plug on the other end, gray is the middle plug. In practice, less than half of the PATA cables I've seen have been properly color-coded, and some of those that have refuse to work the "right way". What's PATA one letter away from?



Whoever started the "Someone call the waaaambulance" softlink, you are my hero.