Vista: How to repair corrupt System files -- Avast Antivirus

[sbp1]

My wife's HP laptop had Vista running with Avast antivirus. Recently,
internet connection has stopped responding. Googling reveals this is a
result of an Avast bug. She uninstalled Avast, problem won't go away. Tried
all the fixes. Seems to have corrupted something in Vista. I don't see any
way to "repair" Vista. How can I do a repair installation (like I do for
Office corruptions or on XP)? One thing we want to avoid is having to do a
clean install/deleting all existing programs/docs.

PS: She can't find the Vista disc that came with the laptop (maybe -- so
many of these things no longer come with discs), but does have a valid Key on
the laptop.

 

[Guest]

Type in Start - Run

sfc /scannow

let it run to the end.