Try disabling Avast from starting when you boot your computer. If it starts much faster you'll know the cause of the problem. If not you'll need to investigate further.
Go to Start > Run.
Type 'msconfig' (without the quote marks) and hit 'Enter' (or click 'OK')
Click the Startup tab.
Click to remove the ticks alongside any programs you don't want to start at boot-up.
Click Apply' and 'OK'
Restart your PC.
You'll see a message telling you that you're using Selective Startup Mode. Put a tick alongside 'Don't show this message again'
You can easily reverse your choices by replacing the ticks alongside any programs you want to boot at start-up.
Chris
PS: Using the security clean-up tools within CCleaner on a daily basis won't cause any problems. (I use 'Free Internet Window Washer' every day). However you need to be careful when using software which claims to clean your registry (as part of CCleaner does). I'd never run that option unless I was having problems which might benefit from such a program, and I'd aim to keep the use of such a program to once a year or so.