Hi!
^_^
Could you be more specific with your notebook's model, please?

As you can see at Toshiba's website there are lots of A500 models. I need the model just to make a best research about your problem.

Anyway, you always can try restoring the OS from your recovery partition. How you do that? Look at the first screen that appears when you turn on your notebook. Usually that screen used to show keys that you can press to access to different features like going into your notebook's setup, select boot device, open software to flash BIOS and recovery options like the one you need right now.

If you can't find that, as an alternative option, read a little your user's manual and surely you'll get that information right there too.
Good luck, friend! And remember to go back here and post your results.

Regards from Argentina.
PS: theog posts before me without i'd notincing that.

Anyway... it says "Windows Vista" instead of Windows 7... could that user manual be of an older Toshiba Satellite A500 model? Do the new model that
Tophatguy have the same user manual?

Let's see what our friend
Tophatguy can tell us.