System Failing Before Bios / Occasionally Freezes In Bios

Got a bit of a problem with my housemates pc.A friend gave him some extra RAM, i checked it out and it was crucial 512mb pc2100 CL2.5, and although it didn't match his exsisting RAM it seemed to me that his mobo would only run the FSB at 200mhz anyway so i went ahead and fitted it.It worked fine I then noticed his system temp was running a little high (60-65 degrees), so i took his heatsink off and cleaned the dust and refitted it with some new thermal compound.I added too much and the temp went up. To nearly 90 degrees.I shut it dwon as i didn't want the cpu to pop, cleaned it off, reapplied less compound and figured this would work fine.Now we have the problem. Most of the time: Power on and nothing happens. No bios, no beeps. Occasionally: Power on, i jump into the bios, the temp looks fine (30-40 degrees) and then it freezes right there in the bios after about 30 seconds to a minute.This sounds like a heat issue, but the last temp reading before freeze is 33 degrees.?I've double and triple checked that the heatsink is on properly and thats fine. I followed the official guide on how much compound to use (a blob the size of an uncooked short grain of rice).