avast has been know to wipe Restore Points especially if you have an older version that used a VM called NG.
Go to Device Manager and click the top most entry in the tree, your pc, and select Action > Scan for Hardware changes. See if Windows reinstalls your USB drivers.
Are there any yellow exclamation marks in Device Manager, especially next to your network adapters?
If you have not yellow exclamation marks and scanning for hardware does not resolve the problem and you have access to another computer burn an iso of Fatdog64 to a cd and boot to the desktop. Your Windows partition will most likely be sda2 in the lower left of the desktop. Click once on it to mount the partition. A File Manager will open. If you do not see your Windows files then close the window and click another sdaX icon.
Download this file Fatdog64-702.iso
When you have found your Windows files browse to Windows/system32/config/Regback. You only need to click once on a folder to open it. Do not double click. Are the files in Regback dated just before running Avastclear? If yes then browse to Windows/system32/config and rename the 5 registry hives. Right click and select Rename.
SOFTWARE to SOFTWARE.bak
SAM to SAM.bak
SYSTEM to SYSTEM.bak
DEFAULT to DEFAULT.bak
SECURITY to SECURITY.bak
Once the hives have been renamed click on the sdaX partition with Windows again to bring up two windows. Drag the Windows until they are side by side. On the windows you just opened browse to the Regback folder. Highlight the 5 hives in Regback by pressing Ctrl + left clicking. Once highlighted drag from the Regback folder window to the config folder window. A small dialog box will open. Select copy and click the quite button. Once the files are copied exit out of Fatdog and reboot the computer.
If the files in Regback are dated after using avastclear or if copying the files does not resolve the problem then you probably will need to do a repair install with a Windows 7 install disk.