There is apparently something going on with Hilton’s website because the sign in button (upper right hand corner) seems to be gone at times and only to reappear day later.
On my laptop this seems to be an issue with at Firefox and Chrome. The button does appear on Internet Exploder (which is also my least favorite browser that I never use).
You can do Hilton HHonors award search here that allows you to log in.
The only way to get in has been to do an award search that then prompts you to sign in to reveal your HHonors point rates.
Not sure what is going on with Hilton HHonors log in function. If I would be developer, I would had this issue fixed when it first surfaced.
When members cannot sing in to their accounts to make bookings, they probably go to OTA or competitor.