Mac running slow

My imac has started running extremely slow at times when trying to open email, web pages, my dashboard, etc... I did a hardware test and it said it was okay. I'm currently on Snow Leopard. Any suggestions? Should re-install the os software?

Reinstallation of OS X is seldom if ever required. Slowness can be attributed to many things:

Hard drive space: How much is left?

Anti Virus software: Are you using one? (Not needed.)

Startup Programs: How many do you have?

You might wish to download the free OnyX maintenance and optimization tool from here. Make sure you download the version for Snow Leopard. Also, we do not recommend any other maintenance or cleanup tool as most do not work.

And further whatever model iMac you are using, how much memory is installed?