Grafana dashboard showing "No Data points" whereas promql is returning values

Hi There,
I am new to Grafana , I have installed a new prometheus server and have configuring bunch of wintel and linux server for monitoring. Upon creating new dashboard in grafana, I am unable to see any data coming up for graph. I could see the same graph with same query is fetching details for servers configured in another prometheus server. Could someone provide an insight on this.

Eg:
(wmi_logical_disk_size_bytes{instance=~"$instance",locale!="",datasrc!="",eai=~"$eai"} - wmi_logical_disk_free_bytes{instance=~"$instance",locale!="",datasrc!="",eai=~"$eai"})/wmi_logical_disk_size_bytes{instance=~"$instance",locale!="",datasrc!="",eai=~"$eai"}