HP Compaq dc 7700 conflict with win7

Hello, well please help me, I have HP compaq dc 7700p processor (form factor, ultra slim). well, it works fine with XP , but today, I installed windows 7 ultmae on it. the problem begins from this: when I restart my computer , it goes on restarting and dont want to enter in windows, but when I unplug the power cable and plung it again and power on processor, my processor begins to enter in windows and everything is ok .

please help me
 
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