If you're getting blue screens with a fresh install, then you have a hardware problem. While memory is likely, it could be any hardware part in your PC. I would try this:
Take out any PCI cards.
Disconnect the floppy, and any CD/DVD ROM drives.
Make sure your hard drive is the only device connected, and try rebooting.
Also, an exact error message would be helpful, it usually tells you what is wrong. A memory dump doesn't mean that it is memory.
If it passes Memtest86, try what I have stated above. If you still have blue screens, it's going to be your hard drive, or memory- because that's all that's left!
Ask the tech what he did to "fix it". Also, when does the error come up? At bootup, during bootup, after bootup, when logged in?