problems with sleep and shutdown, can anyone help please?

macbook pro 10.6.8 - has suddenly developed sleep and shutdown issues.

I used to close the lid and laptop would sleep (pulsing light) - would stay cool whilst in bag, reopen lid to resume work immediately.

Now I close the lid and laptop seems to hibernate, but stay running - I can restart using power button only which will sometimes return from hibernate (showing restart bars), and sometimes restart completely (so losing any unfinished work).

When it is closed in this state the light is solid, the screen is off (I think!) yet the system seems to be on, as it gets very hot and fans run.

I have tried initiating sleep from apple menu - same results. So I can only presume sleep no longer works - I cannot get pulsing light to happen at all.

Also a problem with shutdown - when I shutdown from any menu everything switches off, including the light YET the computer stays on, gets hot whilst in bag - same as sleep problem.

I don't have applecare and the machine is around 2 years old. I've reset the SMC, reset PRAM, created a new user and experimented with different ways of shutting down, removed printers, switched off bluetooth, read many troubleshooting issues etc yet symptoms persist, and nothing has worked yet.

Any suggestions gratefully received, thanks in advance.