Windows not responding after user logon, desktop non responsive

Hey im having some problems after i boot my computer with win7 x64. After the usual startup process which is fine, it logs onto my user and the screen just goes all black.. No taskbar, icons or anything. Mouse clicking doesn't work, and only occasionally i can provoke the taskmamager to work with ctrl, alt, del.. But what ever i click there it just sends me back to the black screen.. Its really annoying and ive considered just formating it, but the windows cd i have is only an upgrade version which i cant use as it just says the system is too new.. And i really cant afford a new win 7 cd.. Especially not with the soon release of win8.. Any help will be greatly appreciated, thank you.

Can you run in http://www.sevenforums.com/tutorials/69585-safe-mode.html ?