Macbook Pro Freezing & Crashing?

Hi all i wonder if you can help,

I have had a faulty logic board on my Jan '08 MBP replaced by apple, all seems to be fine except it keep freezing during applicatons.

For example I could be surfing the net, not other apps open and it just freezes, cant move the mouse/trackpad or anything, have to force turn off, sometimes when I restart the grey apple logo comes up but doesn't continue to boot or it sticks on the revolving circle at the grey apple screen, it is intermittent and may not happen every time I use the computer but it's starting to bug me. Any Ideas?

Also sometimes it's getting burningly hot when just emptying trash etc

Please help if anyone has any ideas/solutions?

Thanks

sounds like a RAM issue. Check system profiler and see if ram speeds match and that the status reads ok. P,R,option,command for 3 chimes at start up should clean things up. Still doing this d at start up to test hardware.

thanks, sorry did you mean press R & option command on startup for 3 chimes?

no, key command stated above, press and hold at start up and do not release until third chime is heard. You must be quick to press buttons immediatley after pressing power.