MacBook issue

Hi.
My MacBook ha just developed a problem where it freezes then 'dies'. It's been doing it for a few days now and happens often, under light use. Once off it beeps slowly and loudly in quite an alarming way, until I press the power button.
A few months ago I did some upgrades on the ram, changed the HDD to solid state and changed the optical drive for a 2nd HDD. The system was working amazingly well until a few days ago.
Does anyone know where / how to start looking for the source of the problem?

I don't know how to get figures, but I can say that it happens after as little as 5 minutes light use from a cold start, so barely warm to the touch. I don't want to rule this out but my gut feeling is that it's not heat.
I would understand an incompatibility issue with the upgrades I did, but I've had 2 months of flawless performance with it.

On restart I get the option to submit an error report, but I can't see any obvious clues when looking at it what is wrong?

Don't suppose anyone has any suggestions on what could be causing this?
I might revert my mac back to factory settings (with hardware) and then try again with the upgrades to locate the problem. The downside to this is I've got everything setup just right now with the operating system on my flash drive and all other files on the HDD so its not going to be an easy revert!