21.5" iMac 09 model stuck on white screen after chime.

Was watching a film on my computer and as i was quitting the apps to shutdown after i had finished it crashed and i waited for ages for it to unfreeze but it didnt so i turned it off by the power button and now it wont get past white screen no apple logo comes up, i have unplugged averything out of my comp (external drives etc) and still not working.