Mac is really slow and I can't get Apps to open When I try to open an App it does nothing. I go online and it is extremely slow. I have tried some of the idea's on here but, nothing has helped. I also tried to download a Clean up program. It isn't compatible for my Mac. I have a OS X 10.6.8
Open Activity Monitor and see if something is using an excessive amount of CPU.

Open disk utility and mark your volume.
Check how much Space is available on your drive.
Verify hdd and volume.