Sounds like its on the verge of getting Ylod, is it a fat PS3 ?

i have a 160gb phat also an in having the same problems i opened it up an cleaned it but its still the same problems so i bought some thermal paste an im still waiting for it to be delivered

BluRay Lens starting to fail sounds like :/

Ylod is a general term used to describe alot of problems that could be wrong with your PS3, theres afew things that can cause it. Your next step should be determing what problem yours is. Quite frankly the best way to do that is realising what the symptoms are, when it shuts off while your playing a game or movie its usually always asociated with the RSX chip and you might need some thermal paste because over time the chip tends to slightly seperate from the board. So if its happening while your playing then its not cause your bluray lens isnt reading the disk. If your having problems during the operation of loading a game or movie however then yeah it is usually associated with bluray lens and you might need to find out which type of drive youll need as certain models run certain types eg. KEM410's or KEM400's. Be careful not to apply too much thermal paste if your going that route as its another common mistake people make, just a thin layer applied evenly. Too much and you wont get much flow through it and if you make that mistake you may need to reball your RSX chip because you realised you just superglued it to the motherboard and your still at square one.

Could it be that your PS3 has overheated beyond the verge of recollection?

If your PS3 is showing a red light and turning off by itself, then that means its overheating.

Give it a break for around a day, air out the house and get rid of the dust and etc including the heat in your house.

But if its a YLOD issue, then your probably screwed, but unlike the 360, i heard that PS3's are easy to fix.

I had a fat 160gb PS3 once too. It had the same problem, I would be playing a game and out of no were it would shut off. 1 Week Later I tried turning it on and it would give me a yellow light and shut back off. I am guessing your PS3 is Very Close to getting the Yellow Light Of Death! :O Hope this helped.