Being logged in to Windows 7 with a temporary profile

This problem occurs if the current user’s profile was accidentally deleted from the system.

Note: This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry

1. Log on to the system by using an administrative user account other than the user account that is experiencing the problem.

2. Back up all data in the current user’s profile folder if the profile folder still exists, and then delete the profile folder. By default, the profile resides in the following location:

%SystemDrive%\Users\UserName

3. Click Start, type regedit in the Start Search box, and then press ENTER.

If you are prompted for an administrator password or for confirmation, type your password, or click Continue.

4.Locate the following registry subkey:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ProfileList

5.Under the ProfileList subkey, delete the subkey that is named SID.bak.

Note SID is a placeholder for the security identifier (SID) of the user account that is experiencing the problem. The SID.bak subkey should contain a ProfileImagePath registry entry that points to the original profile folder of the user account that is experiencing the problem.

6. Exit Registry Editor.

7. Log off the system.

8. Log on to the system again.

Here is an article:
http://support.microsoft.com/default.aspx/kb/947242

I would also like to suggest that you scan your computer for malware/viruses. It may also possible that some sort of malware could have been the cause of this.