P hangs on regular startup...no matter what, after massive USB problem

To start, I am a computer professional, but this has me stumped and I want to avoid the nightmare of a full reinstall.

I am runnin windows XP, SP3.

I
It all started with .NET problems. I needed a certain piece of software to run, that required the lastest .NET though mine seemed to be corrupt. I uninstalled and reinstalled thelatest .NET. Thereafter, I started experienceing massive USB problems...devices just wouldn't work, wouldnt connect. I tried everything in the world to get them to run, but after a while the computer started refusing to even uninstall USB devices. Then it started hanging on startup. It will give me the windowes splash screen, then..nothing. Blackness, with the HDD light lighting up like a time, every second, for an instant. It will hang like this indefinitey.

I have gone through all fixes...disabled every service, every startup item in msconfig, etc etc. Nothing I do seems to work.

It will start just fine in safe mode, but in regular mode....nothing.

I cannot even run chkdsk, as it hangs long before chkdsk can engage.

The last time it was running in regular mode, I did sfc scannow, came back perfect.

I am trying to avoid the absolute nightmare of having to reinstall windows (and a hundred other programs).

Any ideas?