That pretty normal for aging P4 laptops. There is no real cure but I find those laptop cooling pads can get an unit that works for that many hours to run over twice as long (with the cooling pad.)
This problem had us ban any purchase of a Pentium 4 laptop at the office.
Help! My Inspiron 8200 MB was fried and I ordered a new MB (and then some) from a computer shop (it is warranteed). The only thing that was missing from what I ordered from the computer shop was the two-piece circuit board that goes atop the processor, display, and keyboard. Worked beautifully after being put back together. After being on for about 5 hours, I got an error message that the laptop was overheating and it shut down. When I started the laptop back up again the next day, I had a black screen with some suggestions as to why it may have overheated: 1) blocked fan; 2) high ambient temperature. I had neither. This is a Dell Inspiron 8200 laptop with a 2.2 Ghz processor (our old one that broke had a 1.7), Windows XP OS, and I upgraded the RAM from 128mb that this new one came with to 768mb (a 512 and a 256). I did notice that as soon as I put the computer back together again, it seemed to run "hot" after just about 10-15 minutes, even though you could hear the fans running. This never happened to my old Inspiron 8200 before I replaced everything. The computer cover is exactly the same as the old one and all the parts in the new one I ordered were spotless and gleaming. No dust anywhere and a bunch of the pieces had initials on them and they state that they tested everything and all the pieces were working fine and that's why they extended a warranty on the darn thing. Does anybody have any suggestions as to what could be the problem? Did I, when I was putting the thing back together, leave something unplugged. I was pretty impressed with the new computer guts I bought because everything was there and it was just so simple to add the display, keyboard, my hard drive, optical drive, battery and shebang-it worked. Any suggestions on the overheating????