won't go in reverse
 

2000 discovery won't go in reverse all other gear work

How many miles? Have you inspected the xyz switch?

It has 200000. What is the xyz switch

Could be a failed reverse gear switch, it happened to me.

XYZ switch is mounted on the autobox offside below the drivers side which sends gear selection to the trans ECU and they do fail from time to time. I did a write up on here on how to repair the XYZ switch. They are slightly adjustable and need carefully marking when being removed unless you use a setting tool to reinstall. The A/C drain also discharges directly over the XYZ switch electrical plug and this needs extending and moving away with a zip tie, I recollect the size required is about 8mm dia.

Typical xyz switch
Discovery II Neutral Safety Switch STC4452 Transmission Range Sensor 0501209718 | eBay

Rebuild D2 ZF Selector Switch UHB100190 - Australian Land Rover Owners

Genuine NEW Land Rover Discovery 2 XYZ Gear Position Switch - UHB100190 | eBay

Would that not let it go in drive to

No, the drive will be fine but it inhibits using reverse. I had the bad experience of parking nose first towards a huge oak tree and when I went to leave the reverse in the autobox wouldn't play so I called LR warranty recovery and the guy explained the scenario and pulled the truck backwards enough to select D and then followed me home. It was then loaded onto the Harwoods LR recovery truck and taken to their workshops for a new switch to be fitted.