Plesk said something about it being a multiprocessor problem, and their solution is to manually use windows dns and disable bind (which is very unhelpful)
Yes, it isn't a solution. ISC BIND is far more popular than Microsoft DNS Server and people want to use it.
I also tried setting the priority for the named.exe process down to the lowest possible setting, but it gave me access denied.
You cannot set the process priority of windows services running under 'Local System' account using the Task Manager. The procedure for setting the priority for them would be a little more complex and will need customizations:
i) Disable BIND service.
ii) Write a windows service (you will need to consult a programmer), which creates named.exe process with the desired priority.
iii) Install that service and set it to automatic startup instead of BIND.
Actually in normal circumstances, it's not recommended to do it.