If it is memory, then if you have more than one Dimm/Simm try taking one out and running with the other. If you only have one stick, then try using it in another memory slot, or substituting with a stick of known good memory (I realise this may be easier said than done!). If you can get to your BIOS, then make sure that the memory timings are right and you're not trying to refresh too quickly. Just removing and replacing the memory can sometimes clear a fault (there may be a poor contact).
What other symptoms do you have - have you had recently? Any event you can pin down? This may not be a memory problem at all?