PC's do have hardware failures. Some of the more common hardware failures are: hard drives, power supplies, cpu cooling fans, keyboards and mouse's.
Keyboard's and Mouse's are the major pc failure but most users can replace these items themselves thereby saving a labor charge.
Power supplies and cpu cooling fans can normally be replaced within a hour.
A hard drive replacement requires more time due to the reloading of software back onto the drive.
Another failure item is the main pc board. Here I question if the repair is worth the cost of a new board. In most cases of a main pc board failure it might be cheaper in the long run to replace the pc it's self.
For the average cost of these repairs see MY-Fee's.
For Laptop hardware failures other then a hard drive or bad memory, I find it best to leave to the manufacture. The cost of trying to get parts for laptops makes it un-economy for most other hardware failures.