I’m about to install avast in an hour, I am hoping someone can answer me.
I was wondering if avast happens to run a scan immediately after rebooting the computer please, and if so, is there a way to stop it running a scan please?
And what’s the average scan time for 100GB computer please.
Thankyou.
Your question is quite chaotic but
For stop try ESC and scan time for 100GB HD is unknown (it depends on many things)
Does avast run a scan after installation of avast? Some programs have been known to run a scan while windows is loading, so I was wondering if avast happened to run a scan upon loading of windows or not, otherwise I won’t install it tonight.
Auroraspirit 
avast! has a special feature - so called “boot-time scan” (which is quite unique amongst antivirus programs). However, you are asked if you want to run it after installtion. And, you can interrupt it using the ESC key (provided you have PS/2 keyboard, or have USB keyboard support enabled in Bios).
If you are referring to resident protection, yes, it’s loaded together with windows, but it shouldn’t slow down the boot by more than a few seconds
How long does a boot up scan take roughly please? I do own a PS2 keyboard, but I don’t know if the ESC will work and I am concerned that I may “damage” the computer upon loading if I do such.
Thankyou.
There is no set duration it is dependent on your CPU, RAM, the amount of data that it will scan.
If you have a ps2 keyboard (and you have it plugged in before you boot) the Esc key should work. avast is simply scanning and doesn’t do anything autonomously, if an infected file is detected it will require a response (see example image) that is why we mention the ps2 keyboard or USB if the USB devices are enabled in your BIOS.
The scan or aborting the scan won’t harm your system, provided you don’t delete anything that might be detected, send it to the chest, deletion is never a good first option as you have none left. The image is an old one and doesn’t show the Move to Chest option, which is in the current avast version.
Now I get you, thankyou David 
Your welcome.
Hi,
I did an installation on a pc with a usb keyboard, after the reboot Avast did find a virus and when i tied to prompt avast what to do with the virus, the pc didnt respond because, im guessing, the driver hadnt loaded yet, i put in a ps/2 keyboard and rebooted the pc. now the pc keeps on rebooting in normal and safe mode before its completely booted up. i have tried refrshing the OS (XP+SP2) but still get the same problem.
What to do?
You’re right.
Can you make it clearer? You try to boot, receive a message window for choosing how to boot (normal, safe mode, etc…). Is this correct?
Do you have any other antivirus in this computer? Had in the past? How did you uninstall it?