I have the same problem on my Dell Inspiron 9300. I did an inplace update
over a stable XP. Updated all necessary drivers and bios direct from Dell.
Still won't sleep with the same symptoms that you have. I removed all usb
devices, still won't sleep. Contacted MSFT support, they got back to me
within a few hours with the following suggestions: (they didn't work for me
but may help.)
Suggestion 1:
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To work around this problem, enable the USB selective suspend option. To do
this, follow these
1. Click Start , type power options in the Start Search box, and then click
Power Options in the Programs list.
If you are prompted for an administrator password or confirmation, type
your password or click Continue.
2. Under the selected power plan, click Change plan settings.
3. Click Change advanced power settings.
4. In the Power Options dialog box, expand USB settings, and then expand
USB selective suspend setting.
5. click Enabled in the On battery list.
6. and then click OK.
Once you have completed the steps above, kindly check if you are still
encountering the same issue. If the issue remains, please proceed to the
below resolution.
Suggestion 2:
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Examine the BIOS settings
1. Click Start, type msinfo32 in the Start Search box, and then click
msinfo32 in the Programs list.
If you are prompted for an administrator password or confirmation, type
your password, or click Continue.
2. In the System Information dialog box, click System Summary in the left
pane.
3. In the right pane, examine the value that appears next to BIOS
Version/Date.
Incorrect BIOS settings may cause this problems in Windows Vista.
Examine the BIOS settings to determine whether the BIOS is configured
correctly.
For more information about the correct settings for the computer BIOS,
contact the computer manufacturer.