OK here's what I did now : I removed the 256 MB Ram chip. The PC wouldn't even start. Then I removed the 1 GB chip and put the 256MB chip in its place. Now, the BIOS showed up (with the usual CMOS error) reporting 256 MB RAM.

Then I placed the 1 GB chip in the other slot once again to see that the BIOS won't start.

So, the slots are fine, but is the 1 GB chip bad ? Then how did it work on displaying the swoosh effects of KDE 4 earlier ? Why did this occur only after formatting and re-installing Linux ?

It does sound, from the evidence so far, that the RAM module has broken. I have no idea how common or not that is but it seems the most likely explanation in the circumstances.
The only way to confirm it would be to try the RAM module in another PC.

When adding RAM, it is essential to consult the docs for the motherboard, especially for older mobos. Often, motherboards will accept RAM sticks only in specific configurations.

For example, if you have four slots, you might be able to do:

256-256-512-512

but not

256-512-256-512.

This here computer I'm using has 4 GB--1 GB stick per slot for four slots. It would not have accepted a configuration like this: 2GB--2GB--0--0. That's just how it rolls.

273, I'll check that with the shopkeeper.

frankBell, the original config was 256MB in the first slot. I added a 1GB chip in the next and it used to work earlier with KDE 4. After updation (and a few power outages later) it doesn't detect he 1 GB chip.

Should I also purchase another 1GB chip and place it alongside this chip ?

Probably nothing to do with formatting or installing/reinstalling any OS.

Power outages are the more likely cause of RAM death.

Its also possible that the 1GB stick you put in had different specs to the RAM stick already installed.

If the 1GB stick was slower or used different voltages (lower or higher) than the original stick, that can cause the stick to run for a while then die.

Check the specs on your current RAM stcks. If you cannot get another RAM stick with the same voltages and as fast or faster than the original stick, then dont try running both at once.

The P4s are PAE so the 3.something limit does not apply (well, when using a PAE kernel anyway). Not that you'll find many P4 chipsets that go beyond 4GB max, there is only 1 P4 chipset that does IIRC (955X chipset, 8GB max memory).

Well, cascade9 thanks for the detailed reply. I have determined that the 1 GB chip is the faulty one (the original 256 MB one works standalone in either slot).

I'll have to buy a new chip, because I've misplaced the bill for this. But its sticker with the barcode and product ID are intact. Can the manufacturer consider that ? Its Hynix, a little-known Chinese company.

I also read a "RAM repair" tutorial below, but soldering and fixing tiny dirty gold contacts is beyond my expertise.
http://www.memorytesters.com/articles/memory_repair.htm

Usually (of course this differs in different countries) you don't need a bill to get that replaced.
By the way, Hynix (formerly Hyundai Electronics) is from South Korea and is currently the second largest manufacturer of DRAM chips (Samsung is #1) and the 6th largest semiconductor company in the world.

Hynix is actually South Korean, and is one of the bigger memory manufacturers. You need look closely at the right RAM stick, or watch the RAM manufacturers to know about them (kinda like likeon used to be).

As far as I know, hynix doesnt deal with customers directly. To RMA (return merchandise authorization) hynix RAM sticks you need to deal with the whoever sold it to you.

Repairing RAM is NOT fun. To replace a faulty RAM chip means buying a new chip, which is a pain, and takes some time. For 1GB DDR2 sticks it wouldnt be woth it, they are still going for $20 US or less. Anyone with the skills and tools to replace RAM chips would charge more than the stick is worth to fix......even assuming that its just one dead chip, not several, or some other issue, like a dead capicitor.

Edit- beaten by TobiSGD on S. Korea.

I dotn know how things work in germany, but here at least (.au) with any store I've dealt with its 'no recipt, no RMA'.

Here in the UK you don't technically need a receipt (as we call the bill) to return an item to a shop but it does speed up the process and some places are awkward if you don't have one. The store could well be able to RMA the part even if they didn't sell it to you (I've dealt with manufacturer warranties as a third party in the past) so it's worth taking it to the store you bought it from even without a receipt.