I've had this problem for a long time, after I have to shut down by pressing the power button (Or because there is a power failure) my computer starts up again, goes into loading screen, and then goes into a black screen with options like Last Good Configuration and Safe Mode. I don't usually have to turn off my computer by switch, but it does come up one time or another, and it doesn't happen the first time, maybe 5 times or 4. I run an XP, Please help! Is it because of pressing the switch or is it something I did before? I don't think it's virus though.
If there is an improper shutdown (ie you pressing the power button to shut down your computer) it will always come up with that screen when you restart the system. If you know the reason that it shut down (like you pressed the power button) just start the system normally. If the computer did something like The Blue Screen of Death or Memory Dump and then shut down, then you have an issue with either the OS, your Ram, or your Hard Drive. Keep in mind, holding the power button to shut down your computer will eventually cause the computer to not start properly (or at all). Of course if you find that your system is stalling often to the point you need to press the power button to shut it down, it means there are most likely some underlying problems with your computer that you should have checked. *** UPDATE FOR YOUR UPDATE *** It sounds like you haven't had a fresh copy of windows installed on your computer for some time. What I usually recommend to my customers (I own a computer company) is when they start to notice problems occurring on the computer to backup the data they need and to format and reinstall windows. I do A LOT of things on my computer, so I tend to format/reinstall every 6 months or so. After you format and reinstall you'll notice the following things: a) Your computer will run MUUUUUCH faster then before you formatted it. b) The computer will have more available hard drive space. c) The computer will be more responsive. d) And the important thing, it won't crash as much! :-) But like I said, when you format you will lose everything on your computer, so remember to back up everything you don't want to lose. You can either burn it on a CD/DVD, or buy a USB Memory Stick to store your data (which is what I use). If you need anymore help, feel free to message me.
Go ahead and let it go into safe mode. Try to do a regular reboot after. Sometimes lost files will be restored. In the worst you may have to do a system restore or system recovery. Extreme you may have to reimage.
It's probably due to pressing the switch. Computers generally prefer to be switched of by the conventional method of start, turn off and shut down.