Windows 7 shutting down on its own

Having a problem with a Lenovo netbook running W7 32 bit. At random times it will simply shut down and power off with no warning, at first it would run for 20 minutes or so but now it does it before the password is entered at the Windows login screen.

Safe Mode works fine.

Here is what I have tried:
Mains power and battery
Safe Mode with networking (works)
Last Known Good Config
System Restore
Startup Repair
Disabling all network adaptors
Disabling anti-virus
Disabling all non-essential startup applications

Nothing had any effect - any other suggestions before I format and re-install?
Thanks

Do you think it could be a hardware issue or overheating?
Also how long has this been happening? was it gradual or sudden?

Thanks for the quick replies!

Problem started last week, no new installs or updates.

Don't think its hardware since it works in safe mode - definitely not heat either.

I can look in the event viewer in safe mode if it would help?

Ok, tried uninstalling ACPI drivers, no change.

It fires up - goes through the Windows loading process, the light blue login screen comes up and before the enter password box shows it goes black and simply powers off. Had the machine for about 6 months and it has worked fine up until this happened last week.

Now running in Safe Mode, event viewer (Windows system logs) for the current time (last crash) has this error:

Code:

Error 
Event 7001
The Network List Service service depends on the Network Location Awareness service which failed to start because of the following error:
The dependency service or group failed to start.

There are a whole bunch of these 'errors' in the event viewer at the time of the crash.

Code:

Error
Event 10005
DCOM got error "1084" attempting to start the service WSearch with arguments "" in order to run the server:
{9E175B6D-F52A-11D8-B9A5-505054503030}

If none of these solutions work try system restore, restore the pc from its last good configuration. If this doesn't work reinstall windows