Inspiron 6000 needs major help

I got my Dell Inspiron 6000 with Windows XP Professional the summer of 2005 and in November of '07 it started having major problems.
It was blue-screening out of control and so I took out the RAM and put it back in (which had solved my problems a month or so before) and when I restarted it was worse, and couldn't get through the start-up programs without blue-screening. So I tried to turn off those programs in msconfig so I could get it to stay on, and when I hit apply/OK it blue-screened with a very loud, sustained, high-pitch beep. After that it wouldn't boot-up, it went straight to a blue-screen saying a file was missing in the registry.
I took it to my university tech services where they ended up keeping it and working on it for three weeks. They backed-up some of my files, wiped my harddrive, and re-installed Windows.
It boots up now, and I can use a program for a few minutes, but then it will say that the program has encountered an error and has to close. And within five minutes of that, the computer will blue-screen with various stop error messages and have to be restarted.
Here are some of the stop error's I've got recently:

• stop:c000021a{Fatal System Error}
  The Windows subsystem process terminated unexpectedly with a status of 0xc0000005 (0x75e9d309) (0x0053f205)
  
• stop:c000021a{Fatal System Error}
  The Windows subsystem process terminated unexpectedly with a status of 0xc000001e (0x00000063) (0x00c9f1b8)
  
• PFN_LIST_CORRUPT
  
• 0x0000007F (0x0000000D 0x00000000 0x00000000 0x00000000)

I can get you dozens of other error codes from my computer, but whenever I search them they just say very vague things about driver or application errors.
Oh, googling the PFN one led me to a tutorial for using verifier.exe to detect and delete unsigned drivers, but that whole thing threw the computer into a restarting fit and showed no improvement even when moving the drivers around like instructed.

Anyway, the thing is that when they copied my files at the tech center, they copied them based on file extension, so there should be no viruses or anything. Also, I've run three different anti-viral and spyware protection scans and they came up with nothing. And now they don't run anymore.
And since they reinstalled my Windows, it shouldn't be a software problem, right? I took the laptop down to hardware support in October and they opened it up and ran tests and found nothing physically wrong with it. And I've gotten desperate and even tried again to take out and blow on the RAM and put it back in again (ala NES) but no change. I've even cleaned out the fan air holes. Oh, and CHKDSK doesn't work anymore either. It only runs two tests and they go through very quick and find nothing wrong.
The tech center guys told me that I should probably just get a new laptop since this once seems to have a problem deeper than software or hardware. But the fact that it starts up and doesn't beep at me or anything still makes me feel like it's savable. I didn't spill anything on it or drop it, it just started to go crazy inside.
Please give me any help you can, I don't want to buy a new laptop without doing everything I can to try and save this one.
Thank you!

 

Worked on it for 3 weeks, huh? That's a long time. Your harddrive is failing. Best case you need to do a complete chkdsk and tell it to automatically fix errors, mark bad sectors and check unused areas of disk. You can run this from the windows install disk. It's probably best just to get a new harddrive, though. Hey, I can sell you one cheep-ish, I got a bunch that are getting ready to go on ebay. I got a 120 5400rpm, and an 80, and a 40, I think. Of course, they are all used, but they work fine.

 

that happened me about 6 months ago, is your fan going almost flat out all the time? the laptop could be overheating, mine was.

The fan started queaking so i got a new fan and when i opened the laptop up there was a thick mat of dust and fluff covering the heatsinks on the laptop. It was so quiet when i cleaned it and replaced the fan. Not a single bluescreen Since.