Overheat due to faulty / blocked fans
PSU voltages (not applicable to laptops)
Household power surges fridge etc switching on/off (does it freeze when running on battery only?)
faulty memory stick try memtest click here virus or spyware scan for both especially if shutting down with in a few minutes of switch on or internet use
driver conflicts especially graphics cards get the latest drivers for your equipment.
You can run a check on the drive. In explorer right click the drive select properties - Tools tab - check drive.
It may also freeze if there are a lot of windows open at the same time and cpu is at 100%
Or if there is not much spare space on the drive.
Model of toshiba laptop? Most hard drives ae easy to change as located under a cover on the base , some are harder to get at as may be under the keyboard. We can probably find a Youtube video or strip down instruction easy enough.
If it really is the drive then you an image the whole drive to an external drive using the free Macrium reflect make the rescue media from the same program - fit a new drive and restore the image to the new drive.