Windows 7 Freezes Randomly

I am running Windows 7 64 bit and also have a problem with my system locking up randomly. My computer uses a DFI Lanparty motherboard that allows me to boot from different drives. I have a drive with Windows XP Pro that has photo editing software and never freezes, I have a drive with Windows 7 64 bit and Protools that has no internet access (ethernet disabled) that never freezes and a drive with Windows 7 64 bit for everything else that freezes randomly. Since I only have a problem with one of the three drives I first replaced this drive but even from a fresh install I saw no change. I took my system down to the basic components only a hard drive and graphics card and went to slower ram but nothing changed. I have replacement components for every thing in my computer. I changed everything including the motherboard and saw no change. I use Avast Pro antivirus and PC Tools Registry Mechanic. The problem does not appear to be defective hardware. I have installed Windows 7 on 7 machines on my network some 32 bit and some 64 bit and have a problem with 3 of the machines. Two are 64 bit desktops and one 32 bit laptop. I have spent many hours reconfiguring CMOS and trying different drivers to no avail. On one machine I see a blue screen memory dump every few days. I replaced the memory and still have the same problem. I have the CMOS not being cached. I am hoping to see a fix soon. I have hundreds of computer builds under my belt but have been unable to resolve this problem. I welcome any tips from anyone that has successfully resolved this problem. Thank you.