CPU Usage High - Slow Laptop?

system: inspiron 1420 windows 7 issue: suddenly slow system (cpu usage usually raises to 100% when opening any programs such as a web browser, then dips back down when everything is loaded enough) attempted solutions: anti-virus, malware, anti-spyware programs | chkdsk, sfc /scannow |memory diagnostics | adjusting appearance | using task manager to locate highest cpu usage program (none of these attempts have identified the problem.)my system which is a dell inspiron 1420 windows 7 was recently given a clean install to windows 7 from vista. everything was going fine for about two weeks when suddenly everything started to become sluggish.now when i for instance open a video on Internet, the video will buffer, and while that's happening the audio that plays sounds like a droning machine as if it was being disconnected from the matrix, ha. after the video loads enough, the sounds remains normal. not only that, but the mouse will stop, stutter, freeze, then continue after the video has loaded enough to where the mouse can move again. i'm also experiencing freezes on this machine, and usually when the computer does freeze the mouse pointer disappears.

i have already tried many things, such as running anti-virus, malware, and anti-spyware programs which had all come up with no threats. i've run chkdsk, sfc /scannow (which did in fact find corrupt files, but they were unable to be repaired. if anyone can tell me how to repair those files that cannot be repaired, i would appreciate it), and i've also done memory diagnostics, all of which are not identifying with the problem i'm having.