Pentium 4 with Hyperthreading based laptop is well known for this. You can sometimes help but never fix the LOCKUP issues by a total tear down to where you pull off the CPU heat sink to clean off the old heat sink compound, put new compound on then clean up as you build it back up.
You can also get some more use by running a speed program like SPEEDSWITCHXP and forcing the machine to its lowest clock rate all the time.
The other great life extender for this laptop is to find a low speed P4 like the 1.8GHz or lower and put that into the laptop.
It will be working fine then suddenly freeze up. I have to manually switch off and restart and then back to normal until the next time.
I have blown with compressed air, the air outlets and the fan inputs. Fans and heat both normal. Prior to blowing out it was getting quite hot. I have run the Product Recovery disc and re-entered information. I use AGV, Spybot search and destroy and Spyblaster.
I hope someone can help me as I don't feel like replacing it with a new one just yet.