Just FYI.
1) Your laptop has a factory recovery partition that the other members have been talking about. Using this, you can revert your machine to the state in which you first unboxed it. For this you need to launch the Toshiba Recovery app from within windows or by presiing a special key at boot such as F11. But check at the Toshiba website/ forums or your manual, what exactly the procedure/ key is. No reactivation of windows will be required.
Remember that this will reinstall all the bloatware (Toshiba stuff, good and bad), your laptop came originally loaded with. If that bothers you, you can use a tool like PC Decrapifier to get rid of the stuff you dont want. Also, back up your data beforehand.
2) You havent told us exactly why you want to reinstall. If you want to have a clean install without any OEM stuff on it, then step 1) will not help. In that case, borrow a dvd from a friend, do a CLEAN INSTALL of the same version that your computer came with, then activate using the COA sticker key at the back of your computer. You will need to call MS for that.
Activate Windows 7 by Phone