PC won't boot after RAM upgrade

I hope someone can help. I own a Packard Bell I-Media 5053 desktop PC, which I've had since the back end of 2002. At the time I thought it had a decent spec!!

Gigabyte GA-8SIML ver 1.0 ATX motherboard.
Intel Celeron 2.00 GHZ cpu.
SIS 650 chipset.
Originally 1x 256MB RAM.

So i decided it was time to improve it a little by upgrading the RAM. So i used the Packard Bell website to establish what i could use. I also used the Corsair website, and eventually bought 2 x 512 Micron DDR PC 2700 333Mhz 184 pin non ecc.

I took out the old RAM and placed both the new ones in the two slots i have available, made sure they were in properly and fired up the PC, it went through its usual start up, but never reached the microsoft screen. It came up with the following error message, Windows could not start because the following file is missing or corrupt "WINDOWS\SYSTEM32\CONFIG\SYSTEM"

So i took the two new sticks out and replaced the old one and it fired up as normal, with no error messages. So i then tried each new stick in the first slot one at a time, and hey presto each tiem the PC fired up and recognised the new RAM. So I then tried each new stick in the second slot on its own and again it fired up properly both times.

So I now knew that the two new sticks of RAM were ok and also the two slots were fine. So i tried again and once again I got the error message.

I've searched high and low on different websites but have not found an answer. I cannot change anything in the BIOS due to the restrictions placed on it by Packard Bell. I have used the CLR CMOS jumper and this doesn't change anything. So to be quite honest I'm stuck.

So please someone throw me a lifeline.