If you have deleted partitions by accident, do not create another partitions, just leave it blank.

If you have deleted files from the recycling bin and you realize you needed it, do not save anything to that drive. Because Hard drives do not actually erase data or partitions. When you erase a file from the operating system, it just marked on the drive as deleted. When your system needs to store more data on that drive, it will consider files on the drive marked Deleted as being free space, and it copy over them. If that happens then you are in big trouble.

This rule also applies for partitions, since partition information just presents the operating system with a way of addressing the space available on that drive. If you delete a partition, everything from will be gone. because there is no partition information, no data can be read by the operating system. Your data will be on the hard drive but operating system can not see that. Data-recovery programs can see that data by scanning hard drive.

The Best thing to do in a data loss situation is to make sure no more data is written to that drive. If you have just the one partition and it's fried, you can't boot normally to the operating system.

The best option is to transfer your hard drive to another computer. Transferring the Hard disk drive to another computer is best because it will prevent the drive from being over written, and potentially allowing you to retrieve files from the disk just by using Windows Explorer to look through file structures. If you have damaged or erased important operating system files, but the partition information is still readable Windows will not boot.

If you can not physically transfer the hard disk to another computer, The simplest way to gain access to the files on your hard disk drive with a DOS boot disk and then use a DOS compatible file recovery program.

If you have only one hard drive with a single partition that is no longer bootable, file recovery becomes more difficult. Because most recovery programs will need a place to copy recovered data, and if you are using the same drive which has the lost data on it you will be destroying more data than you save.

It is a better idea to install a new hard drive onto the current system and save the recovered data on new hard drive..

There are several programs such as Ontrack Easy Recovery, Winternals Disk Commander, Active Partition Recovery and Active Uneraser that will boot your system straight into DOS, then perform file recovery.

If you have installed your damaged hard drive into another computer, or if you have put a new drive with a separate Operating System into your current machine, you now have a many advantages:

You can attempt to access your lost data normally through Windows File Explorer. This will not work if the partition information has been changed, since the OS will not 'see' the logical drives.

Now you can safely play with recovering your files, since you now have a completely separate hard disk drive on which to put recovered data without compromising the damaged hard drive drive.

Here is the tutorials of Freeware Data Recovery Programs: