My 99 Jeep Grand Cherokee now wont start. Anyone have any ideas? The engine is a 6 cylinder 4 liter. Help!!! It just turns but doesnt fire

How many miles? If 80K +, consider a CPS (Crankshaft Position Sensor) which can cause numerous issues. Check out the Cherokee section for a lot of info and some how-tos.

Did it quit running suddenly, or get worse as time went on?

the neutral safety switch would also give you the same symptoms. They re easy to replace, but expensive, so I'd verify that as the cause.

Great point Seosamh, and Welcome to AF.

There's actually a good couple of threads on the Cherokee forum about cleaning your NSS (neutral safety switch) which makes the repair a 0 dollar one. Apparently the NSS doesn't go bad, but just clogs up with stuff.

I'll see if I can find the thread.

You may want to start with this thread: No Start Troubleshoot (http://www.automotiveforums.com/vbulletin/showthread.php?t=687635)

NSS specific link (http://www.automotiveforums.com/vbulletin/showthread.php?t=455871&highlight=clean+neutral+safety+switch)

Those should help out.