PC crashes after new RAM installed

Formally, my PC has only RAM of 512MB.
As I do not know what type of RAM to buy, I brought my PC to the computer shop for the staff to install two new 1GB RAM.
When I brought my PC back, my PC clashed when I scanned my PC with Trend anti-virus/spyware software
(Error message from Microsoft - may need to upgrade BIOS/ clash may be due to incompatility of new RAM installed)
.
I have to bring back my PC for the staff to reinstall my PC with another brand of two 1GB RAM -1GB DDR PC-3200 RAM 400Mhz

The PC doesn't seem to work faster than the previous 512 MB RAM.
No more problem with scanning PC with the anti-virus/spyware software.

But this time the PC just shut down and restarts by itself when I am doing typing work on wordpad on a few occasions.

(Error message from Microsoft - may need to upgrade BIOS/ clash may be due to incompatility of new RAM installed)

I am using Windows XP.
Motherboard - Foxconn

Would appreciate if someone could help.
Also, is there any way to check if the RAM installed is the right type for the PC?

what kind of computer is it? some computers are not compatible with a 1gb ram stick.

My PC has a INTEL PENTIUM (R) 4CPU 3.00 GHz

what company, dell, hp, etc.

Can you give your computer name and model number?

The motherboard is a foxconn, the model number would also help.

When you first boot up your PC, does it recognize the 2GB of RAM in the bios?

When you are in Windows, if you right click on My Computer and select Properties, how much RAM does the General tab say you have?

Your motherboard may not support the memory.
I'm surprised the PC tech did not research this.

Maybe you went over the MAX memory or something... Does it beep when you try to boot?

Thanks to all for taking time to respond my queries.

Company's name : Hon Hai Precision Industry Company Ltd (Taiwan)
Model number: 661FX7MF/648FX7MF/648C7MF (taken from user's manual - no idea which one is installed on my PC)

I bought the CPU (which came with the new Foxconn motherboard and 512MB RAM) on 28 Dec 2005 in Australia.

I have no idea where to look for to check if my PC recognizes the 2GB of RAM in the bios.
Under "view system information" of My Computer, RAM is 1.96GB

No beeping sound when I reboot the PC.

Yesterday I brought my PC to the shop where I bought my RAM the third time.
The staff insert another brand of RAM and told me that if my PC still crashes, then the problem must be due to the motherboard.

Your motherboard supports your 400Mhz RAM. If there was a problem with compatibility, generally your PC would give you an error beeps when you try to start up.

If they have changed the memory and it still crashes, then the memory is likely not the issue.

You could try updating your motherboard drivers, that may save you the money of a new motherboard. You can find the drivers here http://www.foxconnchannel.com/support/downloads.aspx

The manual you have will tell you the socket (478 or 775) to enter into the search.
Flashing your bios might also fix the problem.

If this seems like its too complicated, take it back to the PC techs. They installed new RAM and it should be their responsibility to stabilize your system. Ask them to flash your bios and update your motherboards drivers. If you are still crashing you may have a bad motherboard.