Definitely scan for spyware. That will definitely slow your system down.
I use these:
CCleaner,
SuperAntiSpyware Free Edition. Just google it and it will take you right to the page to download it.
Also dont forget to do
Disk Defragmenter and
Disk Cleanup on your system. That will also take care of some slowing down on your system.
Finally when you store your photos and videos try to store it on a different drive not a C drive. C drive is suppose to be only for programs that run on your system.