Hi Mat,
Please navigate to your subscription in Azure portal, then on left click Access control (IAM) blade.
Click Add -- Add role assignment, next click Privileged administrator roles tab, select Owner, click Next, click Select members, search for and Select your account, click Next, on Conditions tab select Allow user to assign all roles (highly privileged), click Review + assign, Review + assign.
Sign out and back in for the permission change to take effect and then test to see if you are able to Start VM(s). Please let me know your results.
Please click Accept Answer and upvote if the above was helpful.
Thanks.
-TP