Did you just upgrade or install Avast?
Have you tried to reboot your machine to see if it fixes the problem?
1. What is your OS, 32 or 64-bit?
2. What version of Avast did you install? 5.0.677?
3. What product of Avast did you install? Free, Pro, AIS?
4. What other security software do you currently have or did you have in the past on this machine including antivirus (AV), firewall (FW), and other security programs (resident and on-demand)? If they were in the past, how did you remove them (the vendor's uninstaller's tool or another way)?