WIN7 startup hangs at welcome or desktop blank.

my windows7 x64 will not boot completely. I get the welcome screen, with a continuous whirling circle or, sometimes, i get to the desktop, but no icons or task bar. I can't get any response from control/alt/delete to get to task manager. I have easy access to safe mode, and everything there seems normal. I have run AVAST, Malwarebytes, and a couple of other antivirus programs from safe mode, with no virus or malware identified. I have read every post in as many tech sites as I can find, and nothing seems to work. I have already tried going back to earlier restores, and am out of them.

Unless someone can help, I need to backup all my work files and reinstall Windows 7, I guess. I'm concerned that I will not have the drivers I need when I do that. I have a backup Macrium system image, but it's a year old, the external drive it's on clicks like crazy, indicating it's going bad, and I've got a LOT of work on my machine I don't want to lose.
I've already beaten myself severly with a rubber hose for putting off backups and restore disks, so save that...