It ain't *that* cold here. I left my '87 diesel on the street last night. This morning it fired immediately and ran smoothly after perhaps 10 seconds of preglow.

Diesel fuel doesn't begin to gel until the temperature falls into the teens. At about freezing that is definately not your problem.

Your best bet to get it going is to give it an extra-long preglow. The glowplugs continue to heat for 1-2 minutes after the dash light is turned off. Count to 60 after the light goes out, put the accelerator to the floor and hold it, then start cranking. Don't be afraid to crank it for 30 seconds before giving up - the starters on a diesel are designed to take the additional abuse. Give the starter about a minute to cool between attempts.

The poor man's test of the glowplugs is to leave the door open and watch the dome light while preglowing. The light will noticably dim when the glow plugs are heating. When they shut off after a minute or two, the light will brighten. If this isn't happening, then you almost certainly have a problem in the preglow system.

There are a bunch of possible reasons why your car is hard to start. I'll permit some other folks to dig into them here.