First, run spybot, ad-aware and your anti virus application, and clean up any problems that they pull up, and try again. If that fails, then I assume that you either accidently botched up or deleted something that should not have been deleted, or your installation was not successful, meaning you're probably going to have to reinstall Windows.
Oh yeah, if explorer did work at some point and time, you can try a system restore back to that point, rather than a complete reinstall, although you'll have to redo all the changes you've made over that time period, although system restore isn't foolproof.
Intel C2D E6320 / AMD Athlon X2 3800+
Gigabyte 965P DS3 / DFI nF4 Ultra-D
2GB OCZ Gold PC2-6400 / 2GB OCZ Gold PC4000
eVGA 8800GTS 320MB / eVGA 6800GS 256MB
150GB Raptor / 74GB Raptor
2x500GB / 320GB
OCZ GameXStreme 850w / OCZ StealthXStream 600w