hello.
i recently had a virus and decided to reformat my hard drive.
the first few times my computer was booted and rebooted (after installing updates and whatnot),
everything was fine.
but now, when i boot my computer, it beeps and i get a black screen saying something to the sort:

hardware failure:
decreasing memory. your system memory has changed.

when i go to system in the control panel, indeed it shows currently i have 796 MB of RAM when i have actually installed 1GB.

i have never seen this error before.
and before the reformat, my computer worked with this RAM just fine.

im running a Dell Dimension 4550
Pentium 4 -2.52 mhz
Windows XP SP2
dual RAM = 1.0GB

any suggestions please?

How is this 1GB of RAM configured, 2x512MB, 4x256MB.

You could download Memtest 86 and run it to see what condition your RAM is in.

its 2 sticks of 512.

and i am not understanding how to install that memtest thing ?

i will try to clean the sticks or something.

but i really have no idea whats going on.

Memtest has instructions on their website on how to run the tests, please follow them for the best results.

Bascially, what you've got to do is:
1) download the memtest program that's designed for a CD
2) use an ISO burning application to properly burn the ISO format to the CD Here is a free one that I like: http://www.ntfs.com/iso-burning.htm
3) boot from the CD and let the test run. If it starts showing errors, you can stop the test. Errors indicate a likely failure of your memory.
4) you can switch the RAM modules around to see which one's have errors and which don't (running the test on each one).

Just download memtest86 and burn iso file to cd with MagicISO.
http://www.magiciso.com/tutorials/miso-burnwin.htm