Acer laptop goes off after 30 minutes exactly.

Hi,

I guess you are dealing with a virus problem here. Since you just have about 30 minutes of power therefore running a thorough anti virus scan may not reach completion.

I'll advice that 1st pull out the battery and put it back on, boot and format the hard drive.

After doing this please install a very effective anti virus and install your backed up programs.

This would fix your problems.

Cheers

Probably overheating problem.
Get your laptop cleaned in your computer shop and tell them to put new paste. Should not exceed 20eur.

This is typical of a overheating (thermal shut down) CPU problem.
When the CPU overheats and shuts down, it won't bootup again until the CPU cools down. If this is not fixed then the CPU will fail.
This problem is caused by either a faulty fan or the fan and heat assembly is clogged with dust.
Check the fan to see if it spins freely, replace if faulty and clean the dust off the fan and heatsink assembly.
Also apply fresh thermal paste to the heatsink/CPU.

you have set ur computer to sleep or hibernate after 30 minutes of inactivity. you can customize this in you power setting.

Control Panel-> Power Options