Is it the LiveKernelEvent?
After the shutdown, theres a popup about the problem.
So i wonder if it is it...

OR

is it overheat?
sometime i play games my laptop will heat up to 90 degree or something....

how to solve it?

most likely could be overheating. 90 over degrees is extremely hot. make sure the fan is working properly. what model u using?

sony vaio cr35g

I think this model has its fair share of auto shutdown problems due to the inefficiiency of the fan, check out the Sony Website, I think they have patches or updates that solves this problem

if it shuts down suddenly, then chances are heat issue.

if it shuts down with a prompt, then probably a virus or driver issue.

it shuts down without a warning
erm, i can't find the product

Think you need to bring it to the service center ask them to clean the air vent, maybe it's block by dust. or bring it to the sls netbook repair shop and ask them to clean it for you. it should cost about 20 -30 in sls, service center I'm not sure.