I have a snapper lawnmower it starts up just fine but will cut off about 5 seconds later.The problem started a few cuts back the first time it quit I waited a few minutes and re started it and completed cutting my lawn now it will start and cut off after a few seconds.what can I do before taking it to the shop?

What brand engine? What size?

Since we know you have spark, the problem is probably with the air/fuel system. Make sure your air filter is clean and not choking the mower to death. Remove the plug, put your thumb over the plug hole, pull the starter cord, and see if the compression is good. If the compression is good, replace the plug with a new one. Is your gas fresh? Are your fuel lines in good shape or are they deteriorating internally and causing problems with your carburetor? Is your carburetor adjusted properly? Is it time to remove your carburetor, clean it, and rebuild it? Make sure to change your engine oil annually, draining it after the engine is hot. Snappers are good mowers and should last at least 25 years, if you take care of them.