Re-Opening a PO Which is Completed Status on Header

Hello All,

We have a situation in production. We need to Cancel a Requisition. When we try to cancel the Req, it says an error which states "cannot cancel the Req as it was already sourced."  When we try to look up for the PO, the PO HDR Status is  COMPLETED  but the Lines Status shows CANCELED. Is there any way to Re-open the PO or  cancel it so that we can close or cancel the Req.

I cannot view the PO from Add/Update PO page. I can just see the PO from Review PO information page. Any Ideas on how to Proceed ?