there are many factors caused the PC to running slow
such as temporary files ,cookies,etc.
if you can clear these in time
that problems may not happen.
Here I introduce a software that may be help,
Try : www.best-pc-doctor.com
This easy to use,
It'll clean out all the crap that builds up over time (temporary files, old DLL's, etc)
You can also clean and repair your registry.
The first time you use it it'll take some time, but do it regularly and it's quick.
After you've used Ccleaner defragment your hard disc.
These should let your PC run more efficiently.
Hope this helps