I had the same probelm with my PCG-GRZ515G, which I have recently replace with an A-series model.
The GRZ range are equipped with a desktop version of the P4 chip and when there is a large demand placed on the processor (video editing or scanning for viruses) it gets very hot (feel the heat coming out of the exhaust vent on the back of the machine).
When the GRZ laptops are new this is not a problem as the fan assembly (including cooling fin block) are clean. However, over time dust is drawn into the machine and a 'curtain' of dust obstructs the cooling fins. Thus the computer cannot regulate its temperature correctly and the system shuts down to protect the P4 processor etc. I imagine this is what is exactly what has happend to your machine.
The only solution (as Sony will not accept that this is a fault of the laptops design, which it clearly is!) is top open her up (if not in warrenty, if it is send it in to Sony before it runs out!).
Heres how to do it:
On the left hand side of the speaker grill is a small screw (near the Memory Stick slot). Undo this and remove the screw, slide the entire speaker grill to the left and VERY SLOWLY lift it upwards so that it rests against the screen (put something in between to avoid scratches).
TAKE CARE NOT TO DAMAGE AND/OR DISCONNECT THE VERY DELICATE RIBBON CABLES that connect this part to the rest of the computer.
With a compressed air cleaner CAREFULLY attempt to remove dust from the fan assembly and cooling grille assembly (a lot should come out).
Replace everything using the reverse of the above (remember to replace the little screw at the end) and everything should be fine again, for a while......
...... of course over time the dust will build-up and you will need re-doing again, and again etc!!!
Remeber that every time the P4 processor gets so hot that the system has to shut down its lifespan gets considerably shorter due to thermal stress.
As a side note for other users:
This does not effect the GRT models as much as they modified the fan assembly, I am afraid that the GRZ models were particularly poorley designed in this respect.
It is interesting that the new 'flagship' model (the A series) uses a dedicated Pentium-M processor which runs much cooler and has a better fan assemly that of the GRT range (but maintaing air being drawn in from below, not from the side - less dust). So, Sony have overcome most of these over-heating issues. It's just a pity they never admited to their being a problem in the first place!
Still 'swings and round abouts' the HDD is increadibly easy to upgrade/replave in the GR range an extremely hard to replace in the A range.
Hope this helps both yourself and other GRZ users
CW
