I just formatted my computer and re-installed everything, including Avast! 4.0 Home Edition. Now whenever I start my computer, all the Avast resident scanners are turned off (the blue Avast ball has a red “no” sign on it), so I have to manually re-enable them. 
I never had this problem before the format.
How do I get the resident scanners to Stay turned on, even after I reboot? I checked Settings and didn’t see any option for this.
What is your OS ?
This is usually an indication of the presence of another AV, what else did you install after the format ?
AVAST FAQ - Red Circle on avast icon. AAVM subsytem detected and RPC error. http://www.avast.com/eng/faq-other-questions.html#idt_1539 Try this and see if it is applicable.
You report installing avast 4.0, that is really old, the latest version is 4.7.871, if your version is 4.0 I suggest you download the latest version, uninstall, reboot and install the latest version.
I’m still using 98SE.
I upgraded to the newest version of Avast, but I’m still seeing the No symbol.
The FAQ didn’t solve the problem. I’m not seeing any error messages.
Right-clicking and choosing “Start On-Access Protection” does nothing. The only way to turn the scanners back on is to double click the icon and turn on each one individually.
That particular error message is winNT, win2k, XP only.
What about the other question “This is usually an indication of the presence of another AV, what else did you install after the format ?”
What other security based software do you have, e.g. Spybot S&D (TeaTimer), AdAware (AdWatch), SpySweeper, PrevX, WinPatrol, ProcessGuard, etc. ?
If none of the above is applicable then try this:
Download the avast! Uninstall Utility, find it here and save it so you can find it again.
Old Versions of avast! http://www.filehippo.com/download_avast_antivirus/ from this link download the 4.7.844 version of avast and save that too.