Vista - my administrator doesnt work

ok heres the problem
i am the system administrator and the only user on the computer
it even says i am the system administrator.
but when i try to access some thing it comes up with:

Windows cannot access the specified device, path or file. You may not have the appropriate permissions to access the item.

I cant install download or do anything on my computer i cant change my user settings i cant even make another account and i dont know why i havnt istalled anything new onto vista it has just started doing this a month ago have had computer for 2 years and it just starts doing this now!

HELP ME PLEASE!!!

radical step but you must have lost permission to your C Drive, right click the c:/ drive and properties, click on the security tab at the top and edit, click continue on the UAC prompt and click your user name, click on all the unticked boxes below and click apply, it will take a few minutes and a few files will deny access but this will regain control of all your files again and hopefully the problem

um tried ur suggestion but it still doesnt work all the boxes were ticked im running out of ideas and advice and i dont want to have to reformat my computer as i dont have the software disks or vista it all came already installed...

Do the same for the admin.

Got system adminiator to work my own way lol but now i have a new problem!
C:\ is not accessible Access is Denied.
And my Free space and used space both display 0 like theres no hard drive what so ever i cant save or access my c drive anymore and i dont know how to fix it i dont understand i havent done anything to make it like this ARGH getting so frustrated dont have the money for a new computer at the moment!!!

instead of thinking like that, think of a problem as solvable rather than an issue that cannot be fixed, you dont need to replace your computer. heres what you do, click start and type in the search box "system restore" and hit enter, now click on choose a different restore point, and on the calendar, choose a date to restore the computer to before the issue arisen. if its not available, click on show restore points older than 5 days, choose one and click restore my computer. your computer will shutdown and restore, wait until its finished and log back into vista, your desktop will be as it was on the day you set it back to, and your computer will basically be like you had it before this ever happened.

still doesnt work i tried to system restore but it came up with this:

C:\Windows\System32\rstrui.exe
The parameter is incorrect.

i am really starting to worry here as i need my computer to work from home i have my own comic industry from home and i cant save or upload any new work and people will be waiting for me to upload updates!

have you tried logging in on safe mode? hold the f5 key when the post screen comes up with computer specs when you first turn your machine on, and go to safe mode, when it loads up, try and access your files under the administrator account, and secondly before i go to bed, have you installed any programs that change your theme? sometimes this can affect your accounts, for some reason.

yea iv tried everything but iv given up i rung globalpc nd they said that theyll restore my data and fix my computer for $120 so i have to leave it broken until i can get some money to fix it i can still access the net i just cant save my work and so i have to postpone my comics for a wile