A three month old PC should still be under Manufacturer's warranty period. You should be able to get support from Toshiba's customers' service.
Some questions:
If you cannot start, how do you get to do System restore? (and repeated System
restores will not help).
Did you make back up DVD's as emphatically recommended before you started
computing? Or did your PC come with OS DVD's?
Are you up to date with updates?
Your trial anti-virus has expired by now. Did you ugrade?
Do you have anti virus at the moment?
Have you made any contact with Toshiba?
Now, some suggestions:
If you made back up DVD's or if PC came with DVD's, try system re-installation.
If it happens again then you might have recieved a badly installed system
to begin with in which case, you should call Toshiba.
However, difficulty in shutting down and re-starting suggests viral infection. Run
at least two different anti-virus. Start with windows defender (came factory
installed) and another (one that you pay for, like Norton, McAfee, AVG, etc.).
If you are on cable connection, most cable companies provide free on line Viral scan.
If you have one, run it. (run one after another...NOT all at once.)
