Help the New Guy (again)

When I built my system about two weeks ago (w/ help from this forum) I thought that a Duron 750 would be enough processor for me. I OC'd the Duron to 8x117 936, but I want more!!! Now I am upgrading to an Athlon-C 1200. My problem is that everytime I start up the machine it locks up about 15 seconds after booting Win98. The mobo tech support said it was probably heat-related (my new HSF hasn't arrived yet). Do you guys think that heat would cause the lockup that fast? The temp was between 61-64 C when these problems were occurring. I know that that is way too hot, but I couldn't wait for my new cooler.
My system:
Epox 8K7A
Mushkin 256Mb PC2100
Coolermaster DP5-6G11(Coolermaster says it supports Athlon up to 1.1 GHz)
p.s. It is not a voltage or FSB problem. I already changed all those configurations by jumper with no results.

If I were stupid, I would pay twice as much for a processor that is slower too. It's o.k.