Install Prob maybe RAM??

[acog1]

Hiya All,
This may sound like a really dumb question but I cannot get the answers I need searching on the net so here goes.
A friend of mine has just bought a new computer from Ebay, it arrived without an operating system pre loaded so she then went and bought a new Windows XP Home OS, however while trying to load it on the computer suddenly turned itself off, she tried again and same thing happened. So she asked me to take a look, I used a different disk just in case but same prob, I have checked BIOS settings and the system is NOT overheating but still keeps switching off.
The motherboard is a MIS N1996MS-7222 also called a PM8PM-V upon checking the spec of this motherboard, it says it can take DDR2 533 or DDR2 400 RAM and currently in the machine is King Tec DDR2 667 so I think the problem is the RAM, however when I look to purchase DDR2 553 RAM google is giving a link to Ebay and showing the DDR 667 so I am none the wiser as to whether or not the RAM is right or wrong.
Can somebody please help me and let me know if the RAM is suitable or not and if this is likely to be the problem.
Thanks
acog1