I am new here and kind of a novice when it comes to the technical things with computers. Our PC is a few years old now and we have been having a few problems with it including adware/spyware invasions and it freezing a lot to mention a few. It is a philips. What brand i am unsure but i did get a number off the back of the tower if it helps Y6Q3-PV05
I have backed up all my files onto an external hard drive and now i want to wipe my computer like it was when i first bought it from the store. I have no clue how to do this. I have tried searching it on the net and have tried hitting a few keys when it reboots and also tried to format c:/ but i am just getting an error that states c:/ is being accessed by something and can not be formatted at this time. Even though C:/ isn't open to anything besided the format window

If anyone can help me out it would be greatly appreciated.
I do not have any recovery discs or a manual. I have misplaced all the computer books. This computer is about 5 years old.