this hp page has quite a few tips on sleep mode & such-
http://h10025.www1.hp.com/ewfrf/wc/d...t=5097981#N851

could be -
[Step 7: Changing the power settings
Power settings control the computer’s ability to go into and come out of sleep/standby mode. Make sure the power options are set so the computer can use sleep/standby mode correctly.
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Adjust the Power Options from Start/Control Panel/System and Security
The following steps provide detailed instructions.

Click Start , Control Panel , System and Security , and then click Power Options .]
more at bottom of the linked page