light went off in bathroom.I thought bulb had blown but I changed all bulbs and still no light, also checked box switch not thrown, it is an over the mirror light fixture, what do you think problem can be. Earlier in day it had been blinking off and on a few times
I would investigate a bad contact in the fixture first.
Tighten/loosen the bulb slightly. Try gently wiggling the bulb. If the light comes on, it's probably a bad contact.
If the light does not come on. Remove the bulb, and with a flashlight carefully look into the empty socket. You're looking for corrosion, discoloration, a bent, misaligned, or damaged contact. If you see any damage, replace the fixture.
If everything with the socket looks good, you'll want to look for loose connections. Turn off the power, and inspect the fixture wiring. If you don't see any problems, check the switch wiring.
If everything still looks good. Use a multimeter to test continuity through the switch.
If you still haven't found the problem, it might be time to contact an Electrician.
By far the most likely culprit is a loose wire on the bathroom light switch.
Also: a failing light switch, a loose wire on the light fixture, or a loose wire nut in one of the switch or fixture boxes. If this happened in my house I would remove the cover plates over the switches and light fixtures and tighten all the connections. If this didn't fix the problem then I would remove the light switch and test its continuity. Next I would use my voltmeter to follow the voltages from one connection to the next.
Remembering always to turn off the current before actually handling any wires or connectors, restoring current only briefly when using the voltmeter.
However -- I know how electricity is supposed to flow in household circuits and I am comfortable working with fixtures and wiring. If you are not confident that you can work on your electrics safely, you shouldn't do it. Working on home wiring is one area where doing it wrong can not only make the problem worse, it can kill you.
I bring up the confidence and safety issues because your somewhat breathless and all too short description of the problem indicates a possible lack of thoroughness and patience. I could be wrong; perhaps you just wanted to save us the tedium of reading a long rambling question.
Your problem is probably quite simple to fix but if you haven't done electrical work before you should get someone to show you how to do it safely.