Computer wont boot os Disks

[gibblett]

This is for a friends computer, It has worked before because when i got the computer i put win 7 on then something ****ed out so i then put xp pro on and since then it doesnt want to know about any os disks, other bootable disks work just not os disks. I have a problem which i have had for a while now, every time i try to install a new os it wont boot the disk so that i can install it, I have been into the bios changed the boot priority to cd-rom first, i have changed the cables around, i have unplugged everything except the dvd drive, i have pulled the whole computer apart and put it back together piece by piece, i have also crawled the internet for solutions but no seems to give any answer that works, i have put a different dvd drive in aswell and that made no difference either.
I would appreciate any advice that i have not tried so dont go repeating what i have done, i have more than likely forgotten somethings that i have done.

My system specs are as follows

MB: Asus m4a79t deluxe
CPU: Athlon II X4 965 BE
memory: Gskill 4gb 1066
GFX card: HIS Ati 5850
Optical: Asus dvd burner
Storage: Samsung spinpoint F3 1TB

 

[peterjones]

[memory: Gskill 4gb 1066]
This is a late answer, in case somebody else is passing by. Reduce memory to 2gb or 3gb. Better is 2gb.
pj