try this
start pc
hold F8
select safe mode with command promt
when the box appears type
net user administrator /active:yes
a mesage should come up saying successfull
reboot the pc
an account administrator should appear.... IF THIS IS YOUR ACCOUNT THEN GOOD! IF NOT PROCEED
login, go to start
control panel
system and secuity
computer management
users folder
click users
CHECK IF YOUR USERNAME IS STILL THERE... IF SO PROCEED
right click your account and click properties,
ensure the account is not disabled or locked
if the boxes are ticked untick them and save
to remove the main account
repeat the same process at the start however type
net user administrator /active:no