Is this the only node that you're monitoring NetFlows with? Can you see data for the other nodes?
Was OrionNetPerfMon, the only service that was down? Is the "SolarWinds NetFlow Service" stopped?
Can you see the flows (on port 2055) if you use a sniffer trace?
Those are the first few steps.
i checked the server where solarwinds was running. the netflow service had stopped. i run it again and netflow data were seen. thanks!