Your OS has been corrupted or the hard drive is failing.
What version of Windows do you have?
When did it last work?
What did you do just before it stopped loading?
If you have a Windows install CD, you might be able to repair the Windows install without losing your programs or personal data, but if you have a OEM restore type CD, you might not be able to repair without losing the data on the hard drive, so contact Toshiba Tech Support before trying anything.
If the hard drive is failing, you will need to replace it. But you might be able to get the data off the hard drive if you have a USB-to-SATA adapter, and connect this drive to another PC.