XP won't recognise installed RAM!

  fudge 19:03 08 Apr 2008

I'm using Win XP SP2. Until recently I had 2 x 256 RAM modules fitted. One was PC2100 (266Mhz) and one was PC2700 (333Mhz). Everything has been working fine for a couple of years.
Recently I started to get blue screen error messages at boot-up which pointed to faulty memory. So I removed the PC2100 module (as that's the oldest) and bingo - no more error messages at start up. I thought that was the problem. Now I'm not so sure.
I ran it a few days to make sure it was stable and then fitted the working module (PC2700) in the slot vacated by the dud RAM. Result - system wouldn't start, just a series of beeps. So I tried in another slot and all worked OK again.
I figured this must mean the socket was faulty, not the original module. So I put the original module (the PC2100) back in the good slot where the PC2700 module had been - still with me - and it all boots up and runs fine. I have made no changes to the BIOS nor added anything else to the system.
Now here's the query! Windows says I've only got 256Mb of RAM installed (and the speed at which its working makes me think the same). Why won't it recognise that 2 x 256Mb are installed? If its because the first one is in fact faulty why don't I get error messages again?
I'd like to upgrade the old module to 512Mb but I'm reluctant too if Windows won't recognise it. How can I check if the RAM is faulty or get Windows to recognise it?

  Technotiger 19:11 08 Apr 2008

Run the on-line check at click here this will tell you what you have, what your mobo can take, and I believe any problems also.

  fudge 19:25 08 Apr 2008

Thanks. I'd run that test but forgot to mention it. Ooops!!
Funnily enough Crucial's scan recognises both modules so that would indicate Windows isn't recognising it for some reason.

  Technotiger 19:31 08 Apr 2008

Try swapping the modules around into their respective current slots.

  fudge 20:36 08 Apr 2008

Ah, I didn't think of that. I'll try it and see what happens. Thanks.

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