I don't remember at this point if it's been mentioned, but if this is a desktop, and the ethernet controller isn't onboard, then you could try removing that AND removing the bluetooth device physically, and see if the thing boots. Just make sure the computer is powered off and unplugged. And while you're at it, it'd be adviseable (particularly in the winter time) to not do this on carpet, or at least make sure you're grounded when trying - touch something metal while working on it... usually the computer case will do... the metal part, not plastic.
Another option:
1. When you start the computer up, hit <F8> rappidly just before Windows would normally start-up
2. Select "Safe Mode" from the options on the next screen
3. Once in Windows, hit your start button, type msconfig and hit <Enter>
4. Look under Startup, and uncheck everything.
5. Look under Services, and uncheck everything that doesn't say "Microsoft.." for the manufacturer - could disable some of these, too, but I figure it might make this simpler.
6. Hit OK.
7. Tell it "Yes", b/c you want to restart... or either click "Researt now" - I forget the button text.
8. let Windows start up, sign in, and see if it loads properly. If it does, then the issue is with one of the start-up items.
So, if that shows out to be good, you can proceed with eliminating the problem:
1. go back to msconfig, and re-select one service or startup item.
2. reboot.
3. see if issue still gone - if it is, keep working way down lists until you find the culprit.
I realize that may take some time, but it's the simplest route. Personally, I'd try to look specifically for anything related to Bluetooth, network, etc. Also, wouldn't hurt to verify you don't have issues between your security software (antivirus and/or firewall) with any drivers/applications - that can cause a mess as well.
Happy hunting, and let us know how it goes.