DavidR
12
Slow is very subjective, it depends on your system, ram, cpu, avast settings, programs running in the background. With little or no information it is virtually impossible to suggest a course of action.
I would however review what programs there are running in the background and stop those not required. I would also suggest running HiJackThis as it will show exactly what is running, use an on-line scan of your Hijackthis log file try here http://hijackthis.de/index.php to identify what is adware/spyware, not essential, etc.