Monitor displays "No Signal Input" after RAM upgrade?

I have a presario sr1630 with two infineon 256mb of DDR 400MHz PC3200. After about 5 years the computer was lagging so I purchased an additional 1gb PNY DDR 400 PC3200. Everything else operating well. I put the PNY in slot one and moved the other two over to slots 2 & 3. Powered up and the computer just had a constant stream of single, long beebs. Powered down and put back the two original 256. Powered up and the comp seems to be running fine, but now the HP17 monitor just displays Monitor Status No Signal Input, then goes right to sleep. Plug the monitor into laptop, works fine. Plug it into desktop, goes right to sleep. I have disengaged the fan for the intergrated graphic card, pulled the motherboard battery, cleaned out the dust, still same result. Any help would be greatly appreciated.