91 jetta wont fire

I replaced the valve cover gasket on my jetta 1.8 litre and now the engine turns over but will not fire.I sprayed engine degreaser on the block in the front and hosed it off to clean it. I dried out the spark,plugs coil,cap,rotor and distributor,I also checked the fuses and every thing that was plugged in around the engine. What can be the problem.

Check for a spark. I wouldn't waste money on the tester. Heres a quick easy way to test. Remove the #1 plug, then reconnect the plug wire. Put the plug in the lifting hole on the cyl head so that the edges are making good contact to ground. Have someone crank the engine and watch for a spark. If you have a spark, but it doesn't seem to be firing, reinstall the plug, spray some starting spray in the air intake tube and try to crank it. If you still don't get anything, check that the distributer is at the one position at top dead center.