The message you had pop-up says you need to repair your computer could have appeared from one of several type places.
The first is the aggravating that is a adware pop-up (and make fill the whole screen) saying there are problems with your computer of different varieties. Usually it either wats you to call a number and buy a service to clean your computer or go to a website and buy a program to fix the problem. In either case just ignore and close the message. They do not know if anything is wrong with your computer and if you follow their directions you will end up getting worse spyware and viruses from them and you will have wasted your money. Likewise, if you get a phone call saying they need to fix your computer (they may claim to be Microsoft but are not) they will accomplish the same things.
The second could be an advertisement from a product you use for another product they make. Usually these popup as small messages in bottom right corner. Again, you can just close and continue and use any cleaning software you already have. I personally like ccleaner, but there are a number of others that have excellent ratings. Depending on what you installed they may really know problems on your computer. Ccleaner once installed will give similar type warnings.
Usually for these messages the best thing is ignore and if in doubt call and ask a computer expert you trust.