Windows 7: need help laptop shuts down

hello can any body help me with my lenovo g550.. the problem is it shuts off at a certain point.. but when i turn it on it goes on.. what might be causing this problem.. is it the cpu or my grapic.. any way im using dual core intel then nvidia geforce g210m.. is it possible that a virus is causing it..? thanks for help

Did this behavior start after any changes made to your computer, including programs or Updates installed?

Download, install and run a full scan with Malwarebytes.

Install SpeedFan to check your CPU and case temperatures, add fan speed variability.

Reboot computer, tap F8 vigorously every other second at reboot to access Advanced Boot Options,
click on Repair My Computer, accept any offered Repair. If no Repair is offered, click through to System Recovery Options to run Startup Repair to see if any issues are found.

Test your RAM: RAM - Test with Memtest86+

Test your HD using maker's diagnostics/repair extended CD scan. You can google the model listed under HD in Device Manager to determine the make of HD: Hard Drive Diagnostics Tools and Utilities