It sounds as though your computer is in fact failing to resume from sleep (which is why you're seeing the BIOS screen). What is happening is that your computer tries to restore from sleep, fails, and then reboots itself. It then restores your session from the image it saved to disk when you put it to sleep in the first place. (Win7 does much cleverer things with sleep than previous versions.)
This may not be easily soluable. Make sure your Windows is patched to the latest service pack, and if that doesn't help try setting your BIOS options to try the various different ACPI sleep modes.
There are also some settings you can play about with in Windows. Go to "Control Panel", "Power Settings", Select "Change when the computer sleeps" from the left hand side box, then "Change Advanced Power Settings". You can try turning off "USB settings" / "USB Selective Suspend", as your motherboard may not support this. You could also try setting "Sleep" / "Allow hybrid sleep" to off, or if all else fails, set "Sleep" / "Sleep After" to never and "Sleep / Hibernate After" to an appropriate time, and force your machine to hibernate rather than sleep.
Unfortunately suspend and resume have always been pretty flaky, and you may find that your motherboard just doesn't support it that well.
AFAIK selective suspend occurs not only in sleep, but rather after a timeout of no traffic over the USB, so I don't see how that would be related – Jonathan – 2011-04-12T06:20:55.780