Do you have problems starting in the morning?, if the head gasket leaks you will get coolant in the engine resulting in problems starting the engine. Water does not compress and the engine will have trouble turning after standing for a couple of hours. Also water in the sump (raised oil level and lower coolant level).
The first thing to check are ignition, take all plugs out - connect them to the wires - make sure they have ground - let someone turn the key and check the sparks. The next thing is to check the compression, at a shop or with a cheap gauge (accurate enough to see if the compression is the same for all cylinders).
If you are uncertain about doing this yourself get a second opinion (from a better mechanic), some mechanics just don't like older cars.