2001 Chevy s10 door won't latch

Lube the door hinges and lock and striker plate. Then make sure you have clearance between the door and fender.
Check the hatch lock assembly to make sure that the rods that connect the latches are still connected. Lube all moving parts.

If you look at the latch mechanism on the door you will see a slotted piece that will line up with the latch receiver on the door post. When the door is open, this slot should be turned so that it can grab the receiver when you close the door. Try moving it into the proper position while manually pulling the door open handle.

The factory alarm is a content alarm. It looks to see if a door is opened without being disarmed by using the key or the fob. Most likely cause is a door latch assembly that is malfunctioning and sending a false signal triggering the alarm. As a side note: If there is an aftermarket alarm installed, that's another issue and should be taken to an alarm installer for diagnosis.

pay someone to fits it

Remove the door panel and inspect the latch rods for damage or broken retention clips. A video is below of how to remove the panel.

Check and see if the latch on the side of the door is stuck open or closed.

Door pins are a common failure on that series of Blazer/S10's. Also, another point of contention that the door faces is a sticky latch. Basically, the door latch re-latches itself and when you shut the door into the catch, it slams into it and bounces off. An easy fix is a 3 part cocktail of brake parts cleaner. Open and shut the latch with a screw driver acting as the catch and your interior door handle a few times. P'Blaster, open and shut the door a few times with the screwdriver acting as the catch. Finally, a good shot of white lithium grease. Open and shut the door with a screwdriver as the catch several times. Once you feel it is un-stuck, actually close and open the door several times. If you notice the door rising every time it catches, you MUST replace the door pins (cheap fix). If the door still has issues, replace the door latch (and since you're in there, do some PM and replace the actuator as well).

first make sure the bolts which hold the latch mechanism to the door are firmly screwed in. if that ain't it, remove the post which it clamps onto from the door jamb and switch it with one from a back door. close the back door firmly, lock it and never use it again. if that ain't it go to www.getsaturnparts.com and buy yourself a new door latch mechanism and pay an auto glass shop to put it in for you.

Sounds like your door hinges are worn. Pin and bushing kits are available at parts stores, and with a little patience are not awful to install. Installing a pair of these should restore the door to the original height, and allow the door to close properly.

Chances are the door latch has closed without the door being closed.

Inspect the latch mechanism on the door. I suspect you will find that the latch is in the closed position.

Use a screw driver to take place of the normal jam pin in the latch apply tension ( like the tension that would be present normally opening the door) and actuate the door handle.

Make sure to lubricate once you do get the latch to open.