same problem - thought the video was bad because the LED next to Caps Lock and above scroll lock was flashing four times. It turns out that memory Slot 2 must be bad. Here's how I came to that conclusion:
1. Followed all standard troubleshooting tips (removed hard drive, memory, left off, discharged by holding in power button for a minute)
2. Put in one memory module in slot one. System came up with post page.
3. Put in second memory module. System would not post
4. Swapped memory modules, leaving Slot 2 open. System posted.
5. Put memory module formerly in Slot 1 into Slot 2. System would not post.
6. Put memory module only in Slot 2. System would not post.
7. Updated BIOS. Repeated steps 2 - 6.
System consistently boots when...