Hardware Issue(s) But Don't Know Which One

Hello,
I have a Dell Studio 1749 running Windows 7. I had problems about a year ago with it, was fed up with the crashing, etc. and decided to use the Windows 7 Pro upgrade I had purchased. Everything appeared to be running fine for several months, then all of the sudden I'm getting the Blue Screen of Death, Memory Management Issues, too many errors to list!! I have spent the past week formatting and reinstalling only to get errors almost immediately after it boots. I went back to the original Windows 7 Home edition to see if maybe I just have a bad cd that's creating a bad install. I spent a couple of days running through extensive diagnostics. Everything seemed to pass, except in another diagnostic, it tells me there are hardware problems and it will give me a list at the end, to which it never did! So here I am spending way too much time trying to figure out what the problem is and getting no where. Any help in leading me in the right direction would be great.