Car running hot

My 98 deville has been running hot for about 3 weeks. One day I was driving and it ran hot and just cut off on me. I let it sit for a couple of days and now it will not start. It seems like the battery is dead so I had my uncle give me a jump and it still will not start. One mechanic said if the head gasket or the head is cracked it will not start. Is this true? If so I read about something called heal-a-seal that is suppose to fix cracked heads and blown head gaskets. Has anyone else heard of this? The website for heal-a-seal is http://www.heal-a-seal.com. Will someone check it out and let me know if this is a legit product.

Engines with blown headgaskets will usually start but will run poorly to one degree or another. Gasket fixes in a can are generally worthless, especially so on a northstar.
Go back to basics. Will your battery take a charge? When you crank it over do you have spark?
If you do get it started, you have to deal with why it overheated. Do you have a coolant leak somewhere? Is there enough tension on the water pump belt? The tensioners on the Ns are known to get hung up and need to be lubricated.
Do some homework and post back the results.