Reinstalling Windows 7 On Sony Viao (without Disc Drive)

I have a Sony Viao which does not have a disc drive and came with Windows 7 ready installed (installation was done automatically along side the process of starting computer up for first time after purchase). I cannot remember my administrator password which in itself has caused many problems; to get around this, I think I need to re-install windows - but to do this as a function on the computer (i.e. through the 'recovery' option on 'Assist' button/function) I must access it as an administrator. I think I need to reinstall manually through command prompt, can anyone tell me how to do this? Or do they have any additional advice?

I don't have a Windows 7 disc (I've seen the 'creating a bootable USB installer' videos etc, but these seem to require a disc with windows on from which the USB is made, which I don't have!) Hence I think I need to go through command prompt...

My computer literacy is not very good and I am, to be honest, at a loss of how else to get around this problem(and I would rather not spend a massive amount of money I don't have sending it to a PC shop, if i can help it)...the computer itself is not old (it was brought in August 2011) and already once or twice there had been an issue with Windows were an error occured and it appeared to 'forget' windows existed (box appears saying "operating system not found..."), I switched it to 'safe mode' and restarted it and the problem appeared to correct itself but...

Please help! The problem is fairly urgent! I am also worried that it has a virus as I haven't been able to install new anti-virus software (requires admin password for installs etc) and hence I would like to correct the underlying problem of having no administrative authority to correct other problems asap!