Unable to log onto my user account!

I have an admin account, and a guest account. I am able to log onto my guest account but not my admin account.

I am unable to delete my admin account whilst being on the guest account, even though the guest account is an admin.

I am also unable to create a new user account as the error message says, 'The specified account name is not valid, because account names cannot contain the following characters: /\[}":;|<>+=,?* ' although my chosen account name does not include any of these characters.

Also, when I go onto registry and change my profile list (remove .bak etc), when I load up the user profile again, the error 'unable to load profile' comes up

Please help

It wont let me do a systems restore as there is no saved point. It is my parents laptop so im unaware of what they have done. Is there any more possibilities ?

no their wanting me to fix it. I know their passwords to their user accounts as I use their laptop to do college work. are there any more solutions on how to fix this?

does the admin account have a password on it that you have forgotten?

no it doesn't