When avast is set to start on login, it causes the explorer (the control pannel) to crash. When I remove avast from startup with msconfig, the control panel no longer crashes when opening at startup. I’m running windows 7.
2 things:
- av/firewall softwares which are installed in your computer.
- what version of avast are you using right now?
Try from the UI…click settings…click “troubleshooting”…click “load avast services only after other system services have been loaded”. 
I think there should be another solution, users shouldn’t have to do this in order to get it running properly…
As area51 asked, Please let us know the other security software installed, the Avast version , the specifications of the computer…
It is a valid operation: that’s why it’s there in the first place. You can still try to sort things out afterwards, but it gives a hint as where to look for what.
In any case if the PC does not function as it should on boot-up with “funny” symptoms, I would recommend a MBAM scan. Just to make sure. :
I’m sorry but how is loading it after system services going to help permanently? I’m just saying, its better to check for other applications (mainly security suites) that may conflict with Avast than to do this… Also like you said doing a scan with MBAM…
That’s what I’m saying: it is not a real permanent solution - that’s why the entry is found in the “Troubleshooting” section. ;D
But it is a tool for troubleshooting - and doubtlessly a late Avast is better than no Avast, right? 
I’m out of this thread, I don’t want to interfere but just give the input to run MBAM.
Have a great weekend!
Cheers
Steven Gail (aka Zyndstoff)
lol ok ;D thats true, better late than never 
but I still dont understand how running Avast late can help…
But a scan with MBAM should detect if there are any infections that got through Avast…
Enjoy the weekend!
Cheers!
I think we should wait for OP comments… ;D
What I was trying to do is to help the OP by finding out what it “isn’t” to find out what “is” causing the problem. MBAM is another good option. I agree avast at the get-go is best but better late than never. The OP should give more info. Like other security software they have or ever had in the past. Also if uninstalled how was the software uninstalled?
No worries para-noid… Like I said in my first post its better to have known more about the OP’s pc - SW and HW…