I propose the best option is to do what is called a 'clean' install of Avast!
Do all work of uninstalling and installing the clean version of Avast! whilst offline, never online.
If version of Avast! is paid, not free, be sure to get or find the license copy for it before you begin.
Get latest copy of Avast 7.0.1456 here: http://www.avast.com/en-us/index
and get the copy of aswclear.exe here: http://www.avast.com/uninstall-utility
Follow the instructions on this page, and be sure to download this copy only to your desktop.
You might want to have a look at this over here: https://support.avast.com/index.php?languageid=1&group=eng&_m=knowledgebase&_a=viewarticle&kbarticleid=574
and here: http://singularlabs.com/uninstallers/security-software/
Left over remnants of old/never used antivirus programs can/will conflict with the new antivirus you just installed. This would include an antivirus program that came with the new computer but you never used it, say, for example, Norton, with a trial period.
Try to uninstall Avast! using Add/Remove. Sometimes this does not work. Even if it does, there are remnants still left behind.
Run aswclear.exe in safe mode for every version of Avast! you have ever had, beginning with version 7, then version 6, etc. Reboot after removal of each version, go back to safe mode, and repeat for each version.
When ready to install Avast! after the last reboot, install in normal mode.
Use the custom install option so you can bypass install of Chrome.
Just watch for the window that will pop up after completion of install after system restart to ensure Chrome will not be installed. Click finish.
Tip: Anytime Avast! upgrades to a newer build number, (Example: 4.8, 5.0, 6.0, 7.0) always be ready to do a clean install. If paid, be sure to have the license info handy. If free, registering will give you another year subscription.
Reason is, each new build comes with more features, and advanced features at that, so updating within the program is not your best choice with a build change.
Clean install is.