Wrong RAM????

I bought this computer to fix it is an Acer Aspire T690 bout it off of ebay the title said there was something over heating that it just kept shutting itself off. It gets here and i start diagnosing the problem i turn the computer on and it i can't see where it is over heating so i take and i put an ubuntu cd in the cd drive because there is no hdd and nothing so i take one of the hdd's that i have laying around and put it in and attempt to load ubuntu onto it and it freezes and i had to hard power off so then i take the heat sink and fan off clean the cpu and heat sink and apply new thermal paste still having the same problem then i run memtest for about 24 hours and all i am getting is test 7 errors and by documentation that i found on test 7 it isn't a test that will tell you if you have bad ram (Please correct me if i am wrong). So yesterday i havea windows cd lying around and i try to load it thinking maybe Ubuntu just isn't compatible well then i get a BSOD that tells me page fault it nonpaged area so i looked that up and got and idea what that was so then i moved my memory to the other slot i didn't get a BSOD until like five trys but it kept coming up and saying that this and that important file was missing or corrupt so i get to looking online to see what RAM this computer is supposed to have and it is supposed to have ddr2 pc2-5300 667mhz
and it actually had ddr2 pc2-4200U-444-12 so is the ram causing my problem cause i thought i had a bad mobo and bought another to replace the one i have. thank you in advance for any help.