2001 Xterra will run fine for a week or so and then it won't run for about a month. I have no idea where to start looking to try and fix this problem. Please anybody have any suggestions.

how many miles?

V6?

won't start at all or just runs like krapp?

it's has about 100,000 miles and it's a v6 and it won't start at all. it will turn over but not start.

look up timing belt stuff.....could be the problem.

if you have spark and fuel....that's probably it.

I can most likely narrow it down for ya.

no spark? distributor or plugs
no fuel? sending unit.....maybe filter.

otherwise it's the timing belt.

this is all assumption of course........but sounds like the problem