2004 Civic LX ignition lock cylinder jammed, key won't turn, 2003 2005
 

2004 Honda Civic LX 4-door sedan, manual transmission. Same part number for 2003-2005. 140,000 miles.

No issues, then one day the ignition lock cylinder won't turn. Couldn't start the car, move the steering wheel, nor roll up the windows.

Solution was to remove the ignition assembly from the steering column, and take that part to a locksmith to have the cylinder rebuilt for the existing key.

Because I was stranded, I doused the internal lock components with WD-40, inserting the tiny, red tube into the lock cylinder, through the key hole. It started ONCE, got me home, and allowed me to roll up the windows. Once home, the cylinder jammed again. Don't count on WD-40 except as a one-time, emergency solution. Roll your windows up when you have the chance.

I haven't tried this, but a credible source told me that you can remove the black-plastic housing from the ignition assembly at the opposite end from the key hole. This exposes a slot where you can turn with a screwdriver and start the car, provided the key is inserted in the lock cylinder (if it's at or near the halo.) Could come in handy if you're stranded.

To remove the ignition assembly:

Steering column's outer plastic housing comes apart in two pieces. The top piece is clips only. Underneath, three phillips-head screws hold the bottom piece in place.

Remove heavy-duty dark red connector, bottom, pulls out. Remove two bright green connectors from the black-plastic security components, near the key opening, pinch gently to release delicate tabs.

Four phillips-head screws hold the black-plastic security assembly (to the right of the steering column, fits around the key opening.) One of these screws is in a tight spot. I had no short screw driver, so I had to use an extended (two inches) #2 phillips hex insert for my drill, then grab that with needle-nose vise grips and turn it while pressing it very firmly into the screw head. You could also try removing the break-off bolts first (see below).

You may find it helpful to disconnect other connectors, because they're in your way. On top, remove two light-gray connectors, one white connector, held with one tab each. Remove yellow connector, bottom left, plunger style, pinch plunger then gently pull off.

Ignition assembly attaches to steering column with two break-off bolts (no hex head, allen head, or slots for a screwdriver). Best method for removing is small cold chisel and small ball-peen hammer. Cut a nick in the edge of the bolt head, then change the angle of the chisel to be almost tangent, then hit the chisel to rotate the head of the bolt counter clockwise.

(Tried cutting a slot for a screwdriver using a Dremel with an abrasive-cutter disc, but it took much longer, and didn't work, because the sides of the slot were not clean, screwdriver slipped out.)

To remove the lock cylinder, the locksmith knew exactly where to drill a hole in just the right spot. Tolerances are very tight. I could not have done this part myself. He charged me $75.

For reassembly, I cut slots in the heads of the break-off bolts. I used a screwdriver to tighten them.

Replacement by stealership, parts and labor, ignition key won't match doors and trunk: $625
Replacement part at stealership, ignition key won't match doors and trunk: $470
Aftermarket part online, ignition key won't match doors and trunk: $300
Replace all cylinders at stealership so that they'll all match the new key: probably $1200

Fix 2004 Honda Civic ignition lock cylinder key won't turn free
 

Everything bwdrennen said is correct except I didn't pay anything to have it fixed. I removed the lock assembly from the steering column. Then found a video how to remove the lock cylinder. Took punching out a few pins. Removed one of the tumblers that was worn and put it back together. Didn't even have to replace the tumbler. Cost me nothing and did it in Walmart parking lot at 2a.m.

Confirming
 

Just wanted to confirm everything said above and add a bit.

You CAN start the vehicle with a screwdriver if need be. The piece you are looking for is on the other side of the cylinder from the key as said above. Look for a black plastic piece over a white plastic piece. There is a single screw holding it in place on the underside of the assembly, towards the front of the car. Once that is off, look at the white plastic. There is a slot that can be turned to start the car.

Key must be in the ignition, and the black plastic pieces in place over the keyhole. This is the bit that reads the chip in your key. You must also remove the piece on top of the steering column held in place with the breakaway bolts, and take off the entire lock assembly. This will disable the steering wheel lock. I did it with a flathead and a pair of pliers used as a hammer.

I need your help having same problem had to leave car at Walmart. Need some extra tips

Take the botton plastic piece that's on the steering column off, drill the security bolts off the ignition lock mount, remove the little plastic piece on the left side with wires going to it. Start the car using that plastic piece using a screwdriver and get yourself a new lock assembly. Takes 10 minutes.

if I do this, am I able to turn the accessory on before I start it or will it start right up?