As wolf says, make sure that caps lock and num lock are not breaking the password you are typing. Check by typing the password into a program where you can see it, like Notepad, then copy and paste it from Notepad into the Gmail password box to make sure you've got it right.
If you still can't get in, follow the instructions on this page:
https://support.google.com/mail/answer/41078?hl=en
Where it says "You'll be asked some questions to confirm it's your account and an email will be sent to you." that email will be sent to the secondary account you provided when you created the Gmail account. Check that account and, if there's nothing there, follow the extra instructions provided on the link above ("Check your Spam or Bulk Mail folders", "Add
[email protected] to your address book",
"Request another email" and "Check all email addresses you might've used to sign up or sign in to your account")