Let's start a little less complicated, shall we?
Please give us more information:
1. What hardware do you use? Processor and amount of RAM?
2. What is your windows version? (XP, Vista, Win7 - Service Packs installed - 32 or 64 bit)
3. Any other Antivirus/Security program or Firewall currently installed? Which?
4. Any other Antivirus/Security program or Firewall previously installed? Which? Uninstalled?
5. What version of Avast did you try to install? (Free 6.0.1091 ?)
We'll continue after this information has been given.