As you know the life span on these things is finite. You can try reinstalling the OS but since you seem to know about the cleaning the next thing to try is a LiveCD (see google for many).
My Thinkpad T40 has suddenly started to freeze sometimes during start-up.
If I'm able to get it started then it will freeze when it feels like.
I'Ve tried changing the battery, the ram, hard drive and also making sure the heatsink on top of the processor is making contact with it.
I think it is either a heat problem or bios problem.
any suggestions would be appreciated.