Hi,
Here is a quick check you can try. First, check if your free trial credit already expired, because Azure will disable the sub after the 30 days and the fix is to upgrade it to pay as you go. This is the normal step to make the sub active again. Next, check if you hit the spending limit. When the limit is reached, Azure also disable the sub until you remove the spending limit inside the portal.
Also make sure you do not have any unpaid bill or card problem. Past due or blocked payment can stop you from reactivating the sub, so updating the payment method or paying the bill usually fix it.
If all of that looks fine but the reactivate button still stay grey, it might be a backend hold. In that case you need to open an Azure support ticket under subscription management so they can clear it.
For more information about why reactivate option is greyed out, you can visit this link:
I hope this helps!