Why won't my Windows 7 run unless I go into safe mode then hit restart?

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http://superuser.com – I had a problem last week whereby Windows 7 would get stuck on the Welcome screen. I then tried to go into Safe Mode. Everything up to CLASSPNP.SYS would load then the the computer would get stuck for about an hour, but Windows would finally run in Safe Mode. Then when I press restart (without actually doing anything in Safe Mode) I find that I can run the Windows normal mode without too many problems. The only issue I encounter is that one of my two hard drives is not recognized. I later discovered that the hard drive was not recognized in BIOS either. Why is this happening? Can anyone sug (HowTos)