Win7 Installation Saga

Did a Win7 clean install on a Dell PC which met MS standards (by their checking program) with the exception of the audio card. Replace it with an approved audio card. Installation of new audio card went without problems. Then it started..

Second day, mouse stopped working. Purchased MS mouse, but wouldn't install. Changed to second MS mouse and appears to be doing okay. Within the next two days, while reading a newspaper the screeen went blank and the PC froze. A hard restart got it runnig again.

Since then the screen will freeze occasionally, programs will close while using them, (we won't talk of Google Earth!) and the mouse frequently will not move. Could not install MS
Security Essentials. Does not connect with the network sometimes, cannot drag and drop files & folders, cannot group start button icons in subfolders, IE icon on task bar cannot be removed, search function requires 5 steps before searching and doesn't find files I can locate manually, when opening 'computer' I sometimes have 2 C drives show with same files in both, and yesterday when Win7 started, it opened C: drive showing contents when it finishes starting.

Methinks I have a problem! I have a 1200 page book on the ins and outs of Win7 and cannot find answers to these problems after a month of trying the book and internet forums. I've updated all drivers, programs and all hardware is approved.

Is it possible to 'repair' Win7 installation without reformatting and starting over again? If I have to start from scratch, I think I may return to XP (if possible after Win7). While not a techie, I have been in computers since you flipped switches to program them, so have a decent understanding of them. Currently manage about 10 PCs for others, but they are all XP machines.

Don't really want to go back to XP as I've purchased 2 Win7 upgrades but am a bit afraid to risk my main PC with Win7 until I get the first one running correctly.

Would greatly appreciate knowing if I need to scrap this install and start over again or can this installation be 'repaired'?

Thanks, JoeB