SAM i had the same probs. My pc temps would go as far as 90C. I have the same p4. After two days the temps used to go till 108C and at that temp pc automatically switched off. Problem became so bad that 108 will be attainted in just 2-3mins of pc booting up. I also cleaned the heatsink fans and applied thermal paste to no avail. I even got a new fan for 150Rs and still problem was there. Remember I was telling that my games lag and stutter on my new motherboard it was due to over heating. I finally bought a new processor and got a replacement for my MOBO from Gigabyte. Now temp is 50C max. Even during games it does not exceed 50.
Sam your MOBO also may cause processor to over heat. Press del when your pc boots so that you go into the BIOS settings. In it go to PC health status and record the voltages and temperatures there. Speedfan has a tendency to show wrong voltages as I have been using it from 2-3years. Also confirm by using HW Monitor which is better. Finally SAM leave your case open. I used to do this when I was using PC so that it did not over heat. Does your cabinet have side fans? If so see how fast they are spinning and clean the dust on them. Use a blower to blow off dustfrom heat sink.