Welcome to the Forum @Renee_Hasseldine and sorry to hear you are experiencing this issue!
I suspect this might be connected to a bug other users are also experiencing. In order to better understand this issue, would you mind testing these troubleshooting steps and let me know what the results are?
Can you please test Asana on a different browser and incognito windows?
Can you please clear your browser cache and cookies and try to log in again?