my iphone just shows the apple logo

I tried to completly reset my iphone (deleting all files) but it just shows me the apple logo i tried to shut is down (hold the sleep/wake button) no reaction

I tried to hold the home and sleep wake button for 10 seconds just the apple logo is back

AND the iphone is not shown under Mac OS X 10.6.2 or itunes and it is not shown under windows

WHAT can i do to get i back to life???

thanks for your help!!!