"I'd put it into Sleep Mode, after awakening it, the Windows Log-in screen doesn't show up."
That's user configurable and not hard coded. Try again to set it up that way.
As to the wake up issue that's not unusual if a program or driver answers with "I can't sleep now." Troubleshooting that is not a lot of fun. Try this -> http://www.google.com/search?hl=en&q=vista+sleep+troubleshooting&btnG=Google+Search
As you find out, it's not a click here, bang it's dead issue.
Bob
I have an HP Pavilion a6130n Desktop PC that's running on Vista Home Premium. AMD Athlon 64 x2 Dual Core 2.60 GHz and 2942 Mb RAM. This problem started about 2 months ago and I gotten the PC in August. Whenever I'd put it into Sleep Mode, after awakening it, the Windows Log-in screen doesn't show up. And also when I put it to Sleep Mode at night, it'll start up again a few minutes later. I have a wireless internet adapter, also.

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