The Privacy & Security Community is loaded with examples of this exact question. It is best to look through that Community more closely. In addition to that, please take a look at the following Documents:

Using the Tiered (or Layered) Approached to Protecting Your Computer

Individual Programs ( "Layered" ) Approach to Security

Avast should NOT be taking that amount of time to "load" . There have been recent

"Threads" on the Avast Support Forums on this subject ; have you looked through any of

them, like http://forum.avast.com/index.php?topic=37148.0 , which has a link to the earlier

http://forum.avast.com/index.php?topic=35172.0 !? The Rootkit Scan mentioned by

piyushsingh should be taking seconds, NOT minutes, according to those threads .

Should start by letting us know the SPECIFIC Version Number, most likely either

4.8.1201 or 4.8.1227 !? Any since you have been trying various antivirus programs,

the Question arises did you ALSO use their "Removal Tool", IF it exists, to completely

Remove the Other AV's ; this applies SPECIFICALLY to Norton !?

NOTE : IF you have the latest Avast 4.8.1227, should Definitely NOT Install the Online

Armor, which is considered a "classical" HIPS ( Host-based Intrusion Prevention System)

program, which has a long "Learning Curve" , because there are MAJOR CONFLICTING

PROBLEMS with Both programs on a computer . Instead of Online Armor, I recommend

you look into using "Defensewall" from http://www.softsphere.com IF interested in those

"Types" of programs .

P.S. To access Avast's program Settings, you RIGHT-click the blueist "a" icon, then click

"Program Settings" and go through each "Item", making your Selection .