Never a bad idea to learn stuff, and opening it up will certainly be a learning exercise

As Matt says, the CPU could very well be soldered in, but I have another question - considering that CPU's are generally fairly robust once on the board, what caused you to conclude that a new CPU would fix it? I've seen lots of things fail on notebooks, but I don't recall ever having seen a CPU failure - doesn't mean it can't happen, but I would think it would be quite rare.

If the machine is quite old it may be as simple as the CMOS battery - I've seen some strange behaviour in notebooks with a failed CMOS battery - stuff you don't see on desktops. However if it's that old then it most certainly is not a good candidate for Win7.

A lot of Toshiba's will not start if the main battery is dead (as in stuffed - won't hold a charge), I haven't seen this phenomenon in HP's but that doesn't mean it couldn't happen - trouble is, a main battery is an expensive part to replace just on the off chance...

It's worth looking for leaking electrolytic capacitors - haven't had this problem in a HP, but have in lots of other brands... The cap(s). will be slightly swollen and could have a brown stain in the stress relief lines in the end of the cap.

--=-- My credo: If it's worth doing, it's worth overdoing - just ask my missus, she'll tell ya laugh --=--
You're only paranoid if you're wrong!