Weird Memory Problem

I had a virus removal today on an HP computer. I'm sorry, but I don't know the exact model right now. After the virus removal I noticed that it needed RAM. I had already called the customer and was expecting him within the hour, so I went ahead and was trying additional RAM before the customer arrived, so that I could be prepared and show him the difference in speed once the additional RAM was installed.

It already had 256mb DDR installed already, and I was going to add another 256mb stick to make it dual channel. It recognized the memory, but when booting in to normal mode it blue screens and restarts the computer. It happens so quick that I cannot read the blue screen for any technical information. I tried another stick of 256mb DDR, and I even replaced both sticks with 2 - 512mb sticks and it did the same thing. I tried it with only 1 stick of RAM in it (just like it originally was with the 256mb stick) and it still blue screens.

Now... I can boot in to Safe Mode with both sticks of RAM installed, and I tested both sticks with memtest... everything passes with flying colors. It just acts like the operating system will not allow it to run any more memory than what was originally installed. Would this be a BIOS upgrade that is needed? Or possibly one of the viruses that it was previously infected with is causing this? I am stumped at the moment and my only option is to try the BIOS upgrade, or completely reload the Operating System with the full amount of RAM installed before the reload begins. I have not seen a virus that does this yet. I'm sure there is a first for everything, but I am just curious as to what this could be. It stumps me that it works fine in Safe Mode, and with a live cd, but will not work in Normal mode with any more RAM than the original 256mb stick.