I have a windows 7 home premium desktop.
I can sign in, no problem, but after I sign in the desktop goes black, also when I try to open task manager, it doesn't pop up on top of the black screen and the cursor disappears and all I'm left with is a black screen.
Any ideas on how to get it working again without wiping my C: Drive ?
Can you boot into Safe Mode? I suggest you then run a malware scan.
If you can't you could try a Windows repair. You probably didn't create a repair disk. But, you can download an .iso file on another computer and burn a bootable Windows 7 repair disk. Just Google "windows repair disk" to find the download file.