Hi

You forgot to mention the year. They are similar from year to year,
though.

Since someone took the head off and messed with the car, there's a good
chance a wire is off or something isn't making contact properly. Reseat
all connectors that might have been unplugged during the head removal,
spraying them with contact spray first.

Also make sure your IGN fuse isn't blown -- it would be hard to believe
that a mechanic couldn't find that, but you never know. Very basic
stufff, but never ignore the obvious.

To start troubleshooting, disconnect the coil's primary and put a small
12V bulb across those contacts instead. Sometimes you can just leave
the coil hooked up, depending on the size of your bulb but unhook the
coil to eliminate it from the circuit.  After hooking the bulb up
across those wires, crank the car. If you see the bulb flash, the
problem of not having spark is either the coil, rotor, cap, wires or
plugs.

If you don't see the bulb flash, it could be an open or shorted
ignition transistor (usually sitting on a bracket near your
distributor) or open ignition resistor (is well hidden under your air
intake) or whatever drives this (most likely camshaft sensor or ECU,
etc -- all of which is more involving).
To test the basics, Invest in a multimeter and a manual for your car as
the manual will help you find these. It will talk you through testing
these components.

When it gets more involving, it may require a scope to trace the
problem.
This brings me to thinking it hard to imagine that someone that does
this stuff for a living can't figure it out. Fixing a no-spark
condition isn't rocket science for someone that's trained to do this,
especially with the right equipment.

If you feel uncomfortable doing this yourself, I'd try and find a
different mechanic.

Start by getting yourself a good repair manual for your year Altima to
get you a frame of reference. Let this group know how you make out and
get suggestions.

Hope this is somewhat useful.

Remco