Deore dx shifter stops working

Had the same problem, didn't use my bike for longer period. open the shift lever carefully and try something like caramba. worked for me.
sebastian

The tiny moving ratcheting parts inside a shift lever assembly are packed with factory grease at the time of assembly by the manufacturer. Over time, this grease can become sticky, thicken, and harden to the point where the shifter's internal mechanisms no longer move freely. This is especially true of the shifter has remained in a single position over time, unused, like when a bike is put away in storage.

What has most likely happened in your case is one of the small ratchet "pawls" (or catches) has stuck "open", and is unable to "catch" on the rotating part that spools (or pulls) the shift cable that is connected to the derailleur. This is why the lever has very "free" feel through it's range of motion and is not able to "catch" on anyting to shift gears.

Fortunately the fix is usually very quick and simple. Free up the sticky internal parts by spraying a liberal amount of penetrating oil inside the shifter, heavily saturating all the internal parts. Move the shifter through all it's gear positions while doing this and 9 times out of 10, it will eventually free itself up and perform as good as new again.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/john_472b46f833fc3109

Same as halbganz mentioned... I have a Shimano STX (an old group, from th 90s). The bike was stored indoors, without using it for more than 8 years. Front shifter would shift from the small to the medium gear. When pushing the lever again to shift to the large gear, it went freely all the way back, without any resistance. Same thing happened with the rear shifter, I could shift from the small to the middle (4th) gear, but not to larger ones. After tinkering for a while, I put some WD40 in the shifters, through grooves and holes, without removing a single screw. It worked like a charm.

Try the articles on this site:http://www.parktool.com/repair/readhowto.asp?id=117 Also check the derailleur articles.