8935g restarting itself amongst other things -HELP


Sep 5, 2013
Hi Guys,
I am hoping someone maybe able to help.
I have a Acer Aspire 8935g running Windows 7, which has been a brilliant machine.
But it has started randomly rebooting itself or freezing, and sometimes comes back with various blue error screens.
And often it won't come on again (just black screen), unless I remove battery and power supply and hold power button for 30-40 seconds, and then it will boot up correctly.
Ok, so I have tried a hard drive check (because the hard drive often makes a click before it reboots), but this comes back as ok.
I have also run a memtest, and this comes back clear.
I am wondering if it could be a heat issue, but not sure how to diagnose this.
Any advise to try and diagnose this please?