a "Linux Tablet" with "Windows XP" on it?
That sounds fishy...
The dark screen is most likely caused by a failing LCD screen power inverter or backlight.
Either can be replaced by yourself if you have some knowledge of how to open a laptop, unfortunately it is often risky for inexperienced users. (Myself, I would be uncomfortable replacing a backlight unless it was easily accessible... a power inverter usually isn't too much).
Can you give us a model number of the tablet PC so we can assist you in finding parts?
If you can afford to, and if you consider it worthwhile, you may want to consider bringing it to a PC Repair technician.