If you had a PC mechanic look at the PC I would expect them to do these kind of checks so maybe this is a repeat of what they did.

To run dxdiag, click on the start button. In the field right at the bottom of the menu enter dxdiag and hit return. You should get the DirectX Diagnostic tooks, just click through the tabs at the top and check the Notes field, should say no problems found

To see system event logs click on the start button, In the field right at the bottom of the menu enter eventvwr.msc and hit return. It should have in left pane "Windows Logs". Open that and two logs to be interested in are Application and System. Double click on these and scan back to the time of the last freeze. Any Errors list at the time of the freeze might contain a useful hint to the problem, see more info by double-clicking on the error. Your favourite Internet search will be useful to  translate the errors into something more meaningful.