^thanks mominhaq89 ...
just befone ur post...i solved the problem...
actually i wasnt using any application, i simply turned off my cell but when i powered it on it stuck on apple logo...
Solution:
Press power button and home button for exactly ten secconds..
at 10th sec the iphone will power off ..leave the power button but keep pressing the Home button..after some time (more than a minute) leave the home button...the display will turn into greyish colour..and after few seconds iphone powers on...
try it 3-4 times