Hi ,first post here ,recently bought a 1999 glxi tdi .As above the trip computer is not storing the trip milage or any of the other average readings ,ive tried the different settings on the stalk but nothng works .Is this a common problem or something im not doing right .

It's a common fault I had the same issue on my old tdi ... It can be repaired do a search on the forum for instrument cluster repair

You'll probably find that fuse 15 has been removed, which is a quick fix for failing dash gauges. Gets the gauges working again but causes trip to reset every time the ignition is cycled.

yes fuse is removed by previous owner ,what actually goes wrong on instrument cluster ? Is it dry solder joints or is there components to be replaced ?

Dry joints on the 2 voltage regulators in the cluster are the usual culprits, & reflowing the solder often fixs it. There's a really good guide on the forum somewhere so have a search.