I was having the same problem for awhile. It would take 30 min to an hour for it to finally start up successfully. Now, on the countdown it will reach '0' and freeze, locking up everything. I have tried choosing all the choices, but it always freezes. My dad said it's a virus and that he'd have to reformat my computer, but I still have hope it's something less serious, and that I won't lose all my files. This would be the second time I lose my entire life on my computer if he reformats me. I have worked too hard to build it back up to a happy medium to let him ruin me once again, and I do hope someone can please answer us soon.
Also, to answer a question asked before with the original guy with the problem: I, personally, have not recently downloaded anything. To my knowledge I had added nothing new to my computer before restarting, but that's not to say someone else may have done so. Also, I had antispyware run automatically every night at 2am, but I never got results off of it.