Memory test failed!

Hi,

My computer crashes every few hours, no matter how easy the work is (even only internet browsing and text input in notepad).
At restart, XP requires a diskcheck which comes out with a no problems result.

I suspected a memory problem and I did a memory test with the "memtest" utility (MemTest-86 v3.4).

To my astonishment, all the tests came out bad:
INVC failed
LRAND failed
Stride 6 failed
WMATS+ failed
WINVC failed

Now, in these conditions I wonder how the computer can function at all..!

Anyway, what should I do in order to solve the problem?

Thanks.