Gigabyte GA-N680SLI-DQ6 RV2 Mobo help please

Hi. Hope the is someone out there to help. Looked at similar problems on the board but not exactly related to mine.
I recently built a computer from scratch. Here are the specs:

- Gigabyte GA-N680SLI-DQ6 Mobo
- Intel Core 2 QUAD (Q6600)
- 4 GB Kingston DDR2 800 (KHX6400D2LLK2/2GN)
- Gigabyte Geforce 9600GT
- Seagate Baraccuda 500GB HDD (32MB Cache)
- Windows Vista Ultimate (64bit Edition)

When I initially built the system, I only put in 2 GB of the above mentioned RAM. This RAM was recommended by Gigabyte (the list is available at http://www.giga-byte.com/FileList/ [...] i-dq6.pdf)

The PC worked like a dream. The other day I put another 2GB of the same RAM into the PC, thus pushing it up to 4GB. Everything worked perfectly. However, when I switched the PC on last night, the tower powered up as normal. But the screen did not come on. The screen is powering up but only remains on standby. I connected the screen to another PC and it works. I therefore deduced that it could be the mobo or the RAM as my keyboard doesn't power up even though it works on another PC at home. The strange thing is that, every fan connected to the mobo works fine. Do you have any suggestions?

Hi wtfchuck. Thanks for the feedback. However I'm unable to get in to the system. Everything powers up, but the screen is blank.