i'm trying to install the Windows 10 test build on my laptop dual-booted with Windows 7. I had Windows 8 dual booted previously, but deleted it to make space for 10. Upon trying to create a new partition for Windows 10, I get the following message: "We couldn't create a new partion. [Error: 0x984b3f50]." Google turned up nothing, and i'm not quite sure what to do. Anyone know what's causing it?

Edit: Almost forgot, it's also saying windows can't be installed on this drive, and giving me the popup: "Windows cannot be installed on this disk. The selected disk has an MBR partition table. On EFI systems, Windows can only be installed to GPT disks."

I know how to fix THIS one, but I have an abhorrent amount of important personal files and code and such on my machine, and it would take QUITE a while to back it all up, (like 20 hours) but would just backing it up and wiping the disc be the best option at this point?