First of all, maybe the computer was defragmented. For optimum performance, defragment is preferably carried out every six months. It is located in the following location:

•All programs



•Disk Defragmenter
If this does not help to solve the problem completely, then certainly partially.
The computer may load unnecessary programs from startup. You need the item to check the following:


There see the point "startup". Some standard programs, sometimes games, offer their files to add into startup, but that does not in any case not necessary. On this there can safely be deleted only unneeded programs constantly. Of course, antivirus and system processes to keep.
The undoubted source of the load of the CPU can be a virus. If you use a free or "standard" antivirus, then it is possible that the virus operates in your system. Must be checked one-time and free antivirus Kaspersky Virus Removal Tool. If it is something you will find, all you need to remove and install a current antivirus (for example, Internet Security)
Perhaps even, the situation is more simple, and the fact that you installed a lot of programs and use them at the same time. Which means that they just can't cope memory. In this case, you need to either increase RAM or get rid of some programs. Find out what programs are currently in the process, you can use the following key combination (press on them simultaneously): Ctrl+Alt+Del. And watch the whole process of loading the CPU. Thus, it is possible to lose the load by removing some programs.