Upon startup is fine, but after approx 5 minutes the screen will go blank. I have disabled the screen dimmer function but makes no difference. It still seems to be working as it will beep when I touch it.

 

Almost every electrical problem will be caused by a Low Battery. There are many threads in here about that subject.
How old is the battery? How often do you drive it a long distance? Do you have a GOOD battery MAINTAINER? NOT a trickle charger as that will kill a battery.
Battery voltage should be at or above 12.6 volts after resting for awhile.
Maybe have a battery load test. Also, CHARGE the battery at least once, with a good 10 Amp charger or higher, preferably overnight or 24 hours.
Possible but not common is the TSD is bad. Not a horrible job to change and also not too much $$$

 

Thanks for reply. I have had "issues" with Jag before when voltage was not as it should be....... Battery is only 2 years old but I will have a load test as you suggest.

 

I absolutely agree with @Cee Jay . And I have run into situations that the ground was bad. If I recall properly, the ground terminal for the screen is in the passenger footwell, on the outer side of the car, just below the glove box. Mine was loose.

 

Charge it first, then test it as Cee Jay suggests, with a voltmeter if you have one. Charge it using a 10 amp charger and get a full charge. Once charged, let it sit over night. If it reads less than 12.6 volts, replace.
Keep it on a maintainer. Even daily drivers can have problems.