I built my own system 4 years ago. Yesterday i upgraded it with a new water cooler and case. Every other component is the same - windows 7 64-bit, mobo, cpu, ram, video card, hard drives, etc.
The problem i encountered was that i could only get a video signal with a 4 gig stick of RAM installed in one slot. If i installed two sticks (total of 8 gigs), i get a no video signal error. I tested each stick individually and both are fine. The problem is when both 4 gig sticks are installed at the same time. Note that i had those same two sticks installed in the same two color matched slots for the past two years. They ran great from the start and i never had a problem with them.
I confirmed that Windows 7 64-bit is running. I've tried clearing the CMOS multiple times. Other than a mechanical failure during the transfer to the new case, i don't know what else could be wrong. Does anyone have any ideas?