Open up a command prompt window and type
net user admin. The output will be something like this; can you post it here? There are some (perhaps unlikely) reasons why the account could be unusable, so we might as well eliminate those first.
User name dave
Full Name
Comment
User's comment
Country code 000 (System Default)
Account active Yes
Account expires Never
Password last set 4/26/2011 18:03:51
Password expires Never
Password changeable 4/26/2011 18:03:51
Password required No
User may change password Yes
Workstations allowed All
Logon script
User profile
Home directory
Last logon 2/14/2014 21:32:15
Logon hours allowed All
Local Group Memberships *Administrators
Global Group memberships *None
The command completed successfully.
Probably time I changed my password, huh? (This is a fairly unimportant laptop -- the 'couch computer')
The easiest was to capture this is probably
net user admin > somefile.txt and then upload the file here.