Hi Nagaraj,
One possible issue may be with the length of time the device is off. All capacitors must be fully discharged prior to reapplying power.
A second possibility may be related to the CLK pin on the ADS1248. I'm not clear how you are driving this pin. This pin should be tied to DGND if using the internal oscillator. If a glitch appears on this input the device will assume a clock is being applied. If no clock signal is applied then the device will not function as it requires a clock. When you reapply power this pin may glitch in which case the device will halt. The only way to correct this condition is to toggle the reset pin. I would suggest you have at least a pull down resistor on this pin if not connecting directly to DGND to avoid this condition.
Best regards,
Bob B