98 Nissan Altima Won't Idle And Won't Stay Running, What Could It Be?

Could be many things.  Make sure there is gas in it.  It could be a clogged fuel filter and need to be replaced.  In the most extreme case it could be the fuel pump.  I would also check your spark plugs and cables and go from there.  Good luck hope this helps a bit.  I only know this because it has happened to us a million times.