Accidentally gave myself API User permission set and now everywhere in salesforce I get salesforce.com/secur/NoAccess.jsp
is there any way to overcome it consideringI have the only active Admin account?
Remove permission set assignments with the API
this might help.
Login to dataloader and use
[SELECT AssigneeId, Assignee.name,Id,PermissionSetId,PermissionSet.name FROM PermissionSetAssignment] to identify yourself.