1. It shouldn't affect you provided you have saved your original registration key that was sent to you. If you haven't you can register again, if you use the same email as your original registration, you should get the same registration key back. If you register with a different email address you should get a new registration key valid for 14 months, probably the best option since you have less than two months left.
2. Check out the avast help file, web shield isn't a pop-up or ad blocker, it monitors http traffic for infection, stopping the page load prior to it getting on to your browser cache.
Extract from help file:
Web Shield - Provider Settings
Web Shield provider protects your computer from viruses that may infect your computer when browsing the Internet - especially when downloading files from web pages.
If you - possibly by mistake - download an infected file and try to start it, avast! will prevent the infection thanks to its Standard Shield provider (which scans all files that you start of open). With Web Shield, however, the virus will be detected even sooner - during the download of the file. So, Web Shield makes your computer even safer than before.