what do you mean sign? there is no signature required for an efiled federal return. the electronic signature is the prior year's adjusted gross income. you should arrive at a page with an orange rectangle that says transmit. clicking on it efiles your federal return and state (additional info might be needed for state such as state ID info.
We're not sure exactly what screen is not loading.
Did you have a screen called Signature ID where you chose 5 numbers at random and had today's date and your birthday? If so, was it right after that screen that you had the spinning circle?
Did you get past a screen yet that says "I am not a robot" that has a captcha? It may be that captcha screen that's not loading, unless you already saw it and got past it. Have you seen a captcha?
Or were you getting the spinning circle after clicking the orange "Transmit My Return" button? Or is it before you get to that final screen?
In the interest of time I'm going to go ahead and give you some info that can sometimes help you if pages aren't loading correctly.
NOTE: Are you using any ad blockers or script blockers as browser extensions? If so, that can sometimes affect loading of pages or elements on a page.
Otherwise, here's how to troubleshoot:
Or see if trying a different browser (with cookies allowed) will solve it.