I had just factory reset my laptop and just installed sim games again. When I login to the Sims 3 website my account balance (ea and sims3) and cart says null and when I try to go to any part of the website it says page not found. Then I used my windows 8 Internet (app) and it worked fine. I was downloading content I bought but then when it started to download it kept prompting me to sign in and when i did, it would pop up again even though I was already signed in. Ive been a member on the website since 2009 and this has never happened and its really frustrating because I have had problems with sims before just not this and I also downloaded the latest patch before all of this started.
Try to download origin first and use your account to login, if game is showing then fine otherwise remember all Email account and use it.
However, for information Sims 3 is not supported for Windows 8, it can work, but may be with some problems also, just for information.
Okay, try to follow all these steps: https://help.ea.com/uk/article/how-to-maintain-account-security
Use different browsers also like Firefox and Chrome