depends on which operating system you use, normally under Tool. You may google this.
If it does not work, you may consider using "restore" function. Control panel, System and Maintenance, restore your computer to the date when you did not have the problem. Be care, if you restore it to that date, any software installed after that date will be gone. Dont rush it unless you really know what you want to do.
good luck
I am not an IT guy, Period.
