My xk8 1999 stall from time to time, refuse to start again.first after 5 to 10 min. it start again and run normal into the same happened..but sometimes it take time before it appear again. what is the problem ???

 

You don't talk about when it stalls. Does it do it driving at speed or stall coming to a stop? How old is the fuel filter?
Next time it stalls I would immediately press the schrader valve on the fuel rack and see if you have any fuel pressure. The most obvious would be loss of fuel. Some other performance areas to check would be to make sure the part load breather tube is clean, Make sure the MAF sensor is clean and last make sure there isn't excess slop in the accelerator cable at the throttle body.
Worst case is you may have a failing fuel pump where either the pump itself or the connector outside the tank is heating up and will work once again after cooling off.
Check those things out and get back to us with the results.