Modern toshibas have a hidden recovery partition for this purpose which is normally accessed one of 2 ways - try the first method for preference
1. Copy all your files and documents to an external storage device.
2. Shut down the computer.
3. Turn the PC back on and hit the F8 key repeatedly until the Advanced Boot Option Screen appears.
4. Click "Repair Your Computer" if you are not already on it and then press ENTER
5. choose your country and click OK
6. On the "System Recovery Options Screen" click "Restore Application" which is the last option.
7. Follow the on-screen instructions
8. When prompted, click on "Full Factory Recovery"
9. "Next"
10. Click "Yes"
11. you will notice for a while it seems like nothing is happening, give it some time.
12. After some minutes, recovery will complete and you click "Finish"
or
1) Hold down the power button for 10 (ten) seconds to switch off your machine.
Please note: Holding down the power button on the machine forces it to switch off. Any unsaved data will be lost.
2) Press and hold the 0 (zero) key and at the same time, tap the power button once to switch on your notebook.
3) When the machine Starts beeping; release the 0 key.
4) When prompted by the warning screen; select Yes to continue with the system recovery.
5) Select Recovery of Factory Default Software; click Next.
6) Select Recover to out-of-box state. Click Next again.
7) Click Next to Start recovery.
HTH
David
You could also try running a repair disk and see if that will fix it, you can make a repair disk from any working windows 7 PC, as long as it is the same bit version 32 or 64bit - just type in backup in the search box and follow the prompts
HTH
David