2002 Mitsubishi Galant Oil fouled spark plugs not starting?

I recently replaced factory spark plugs with Bosch Platinum 2s, a few weeks thereafter I noticed a minor shaking eminating from the engine Immediately followed by the check engine light. Autozone scanned the trouble code which was P0300 "random cylinder misfire". They cleared it and 2 days later it began again immediately after startup as I was accelerating. I returned to the autozone and the Bosch's appeared to be oil fouled on all 4. I replaced with another set of factory NGK plugs in an attempt to correct the problem at which point it would not start at all with either plug. The car hasn't been subject to any harsh or abusive conditions other than moderate acceleration since all this happened. And with 52K miles and driving perfectly smooth, I cannot locate problem. I'll have it towed to a mechanic very soon, but would very much appreciate any other expert opinion as well. Would a damaged valve cover gasket cause this, or more likely a head gasket? I was unable to determine spark from the ignition coils, but I'm inclined to believe it has something to do with the mechanicals.