As it has not been happening for long, try a System Restore back to before this started.
Failing that, go into Control Panel and check your Power Options to make sure all is OK there. Easier than it sounds, so don't be afraid to have a look, just read what you see on screen.
If the laptop is getting on a bit in age, check your Time/Date (bottom right-hand corner) to make sure the CMOS battery (also known as the RTC Real Time Clock battery) does not need replacing. You might need to get someone to do this for you if it needs replacing.