Windows 7 Cannot Logon to Administrator Account! Windows 7?

[RockStAr]

I installed Windows 7 last week and suddenly today when i logged on to windows 7 and went to user account to change password it said Password is incorrect Please retype.I was surprised since minutes Ago i logged on with the same password.Now, after i googled..some said to reboot and i did after that i was not able to logon even.So, thankfully i had another Limited account But i am not able to reset Password of the administrator account.AND i also found out that i was not able to set password to limited account.Apart from this, windows 7 is showing me a lot of error messages and even as i try to create a new user account it says Invalid characters But I typed not invalid characters.What's Up with My PC.......I even Ran a full system scan with various anti-virus But found Nothing...........

Here's My Pc's Specs..............

Windows 7 Ultimate RTM

Norton 360 Version 6

2GB RAM

Intel D845GVSR Motherboard with Pentium 4 Processor...............

Please Help................!!