Hi,
Shut down the notebook. Tap away at the esc key as you start the notebook to enter the Start-up Menu. Select the Bios option ( usually f10 ) and under the Advanced or Diagnostic tab you should find the facility to run tests on both the Hard Drive and Memory. Post back with the details of any error messages.
Note: If the option to run these tests is not available in the Bios Menu, use the f2 diagnostic menu instead.
Can you also post back with the following details.
1. The full Model No. and Product No. of your G62 series notebook - see Here for a guide on locating this information.
2. The full version of the operating system you are using ( ie Windows 7 64bit ).
Regards,
DP-K