MacBook repeatedly freezes. Fan regularly whirs. Won't go to sleep!

Question

I recently decided to give my iMac some company by purchasing a new MacBook. It arrived and all was well. Then after a couple of days, it froze. I thought nothing of it, held the power button down, switched it back on and carried on without a second thought. However, a few weeks on and it's just gotten worse. It may be since the 10.5.1 update, it may not, but since then it has frozen 4 times, on silly things too, like for example, I told it to shutdown, and nothing happened other than me receiving a message saying logout failed because Activity Monitor failed to close! So i forced it to close and then clicked shutdown again. Everything started to disappear as normal, but the dock remained...My MacBook just sat there like it...After 10 minutes i realised that it was not going to shut down.
Secondly, a common problem i've noticed, but my fan is regularly loud and "whirs". I have tried resetting the PRAM and SMC but nothing has helped.
Thirdly, the very latest issue, whenever I close my lid, it refuses to sleep. I read a post on these forums about the magnet being gone, however, this is so new that if that is the case then I will burn everything I own of Apple's. Annoyingly, when the lid is shut, you'd think it was asleep because the led glows and fades.
Anyone having similar problems or know any possible solutions?

Answer 1

Hrm, used restore discs and now it seems to be ok. However, when i close the lid it sleeps (or seems to), when i lift the lid up again it's a black screen, i hear the machine working and then my desktop is displayed. Which would seem fine, however, in my security tab in preferences, I have selected the option to be prompted for my password to regain access...Yet I am not...I have to enter the password when i restart etc, but not when it wakes, even though the option is set. Anyone had similar or know of a way to fix this?