Upgraded Leopard to Snow Leopard and now the Mac can't cope!

Getting the beach ball almost every time I click anything.
I've downloaded Clean My Mac - which took ages to 'clean' but it's still doing it.

Any ideas what to do ( apart from getting a PC )

 

it's help which model mac?

 

Boot from the Snow Leopard install media. There should be a Utilities or Administration menu item in the menu bar, under this should be Disk Utility, fire that up, point it at the hard drive and select the Repair Permissions option. Go and have a coffee. Periodically check back on it.

Did / do you have time machine enabled? If so, disable it and see if that helps, could be it's trying to backup stuff and it's overwhelming the machine as there are many, many file level changes between 10.5 and 10.6

Check what things are running at Login; Go into System Preferences -> Accounts -> Your Account -> Login Items. Note down what is there, then remove and reboot.

Also, have a look here, see if any apps / utils you use are compatible with SL. It's possible an incompatible app is causing the problem.

You could also fire up the console app, set it to the "All Messages" option, and then use the "Save As" option and pop a copy up of the saved file, it's possible there could be info in there as to what's happening.

Activity monitor is another good thing to run, set it to show all processes, and sort it on processor activity, the item taking the most time is possibly the culprit.