I have installed 256 MB DDR RAM extra in my computer and now my windows XP keeps rebooting on it, until I remove the memory again. Can it be that the problem exists because the old chip is a PC2100 and the new one is a PC3200? They are both 256 MB DDR RAM though.

Hmmn I got a DDR 333 512 and a DDR 400 512 different brands too and it's all working peacefully at DDR 333 because my mobo only goes up to that

Well, there are two things that contradict each other here. One: If the PC3200 says it is backwards compatible to PC2100 then it should work and if it does not say that then it wont work. but Two: Higher speed ram is backward compatible as long as it has the same core (i.e. DDR DDR2 and so on) My next statement would be to check the slots of Ram that you are putting the new stick into with the old ram. You can also try and using the new ram alone and see if it still works. Where does it reboot?? At the WinXP screen or when it is still Posting and do you get any error beeps when you turn the computer on?? You can be amused by the simplest of things. The smartest people in the world, over-look the smallest objects. War does not determine who is right, only who is left.

Never ever mix DDR ram of any kind. If it works you are lucky, and it may work for a while and then "get even" a month later! half the time two sticks from different batches of the same ram won't run right together.

What a load of crap...LOL! Asus A7N8X-X 1800+ @ 8.5 x 200MHz 768MB PC3200 Asus A9550 128MB/128-bit Gamer Edition WinME/WinXP Pro

The computer reboots when windows XP is has booted completely. The moment when I click on for example the start button, it reboots. The new chip (the PC3200) gives the same error when i remove the other one and when i insert the pc3200 alone on the motherboard. the bios recognizes them perfectly. i once managed to click on the system properties in winxp and it showed also 512 MB. After that it crashed :( Help needed since I've bought this chip for quite a lot of money and the guy won't take them back anymore :(

"I've bought this chip for quite a lot of money" I don't know what you consider a lot of money, but if you paid more than $25, you got ripped off. Newegg sells 256MB PC3200 CAS2.5 for under $23, shipped to your door. http://www.newegg.com/Product/Product.asp?Item=N82E16820141165 Use Memtest86 v3.2 to test the suspected bad RAM. Download the file, unzip, & click on INSTALL.BAT, then just follow the instructions. It will prompt you to insert a formatted floppy & will then copy the diagnostics program to the disc & make it bootable. Then you just boot off the floppy & let it do it's thing. Let it run for one complete series of tests (usually about 30 min). If you get any errors at all, consider the RAM to be defective. http://www.memtest86.com/#download0 Asus A7N8X-X 1800+ @ 8.5 x 200MHz 768MB PC3200 Asus A9550 128MB/128-bit Gamer Edition WinME/WinXP Pro