now yahoo is blank
What do you mean? Can't see the yahoo website?
system restore is blank
You mean you can't enable/disable system restore?
Do you mean system restore points are gone?
and it keeps saying JAVA error
When do you get this error?
What is the exact error?
What OS are you using?
What exact version of Avast?
What was the reason to uninstall/reinstall Avast in the first place?