What software did you just install?
What settings did you just change?
Your system was working.
You did something OR you have malware.
If you don't remember what "something" is, then try restoring to a system restore point.
Only if you have used some super-duper cleaner or deleted restore points yourself, do you not have restore points.
Win 7 automatically creates, under certain conditions and weekly, restore points.
Now with that said, use following to pick a restore point that pre-dates the problem.
RESTORE TO A PREVIOUS SYSTEM RESTORE POINT
1) WIN | type SYSTEM RESTORE | ENTER | NEXT
| Choose a different restore point radio button | NEXT
2) Show more restore pointscheckbox (lower left)
3) Highlight the desired restore point
4) Scan for affected programs(lower right)make a note of affected programs
5) CLOSE | NEXT | FINISH
WIN = key with the wavy Microsoft flag on top.