Have you had this problem since you first used the laptop or has it developed since then?
If the latter, it could be a few different scenarios:
1. Malware
You may have installed malware/spyware onto your system. (VERY common for Internet Explorer users) Try running a scan with
Spybot Search & Destroy. Specialized tools do a much better job at detecting this junk than Norton antivirus alone.
2. Norton is miconfigured
Sometimes Norton personal firewall gets a little confused. (My copy gets amnesia regularly) Open the Norton Personal Firewall and make sure internet traffic is allowed, and that your web browsing programs are allowed. You may have to delete firewall rules and re-add them.
3. Bad drivers
Your laptop may have some bad drivers which hang upon shutdown. Check Acer's website for
updates.
4. Windows hangs during the "Saving settings" shutdown stage.
This can be corrected with the
"uphclean" tool.
Hope this was somewhat helpful