I don't use it and know very little about it, but on my system, the utility does not appear to be installed by default if you check the Programs and Features panel, Windows components. I don't if this is the basic protocol, or some type of management utility. But if it is necessary, have you checked those?
Try running wireshark, free from the link below. SNMP should be running on ports 161 and 162 and with the agent running you should be able to see if the agent is making any requests and if snmp is making any responses.
But wireshark should help you more to diagnose the problem than just confirming it "doesn't work". Have you confirmed that ports 161 and 162 are open? Are you able to see that the management agent is sending any request packets? Is the Windows SNMP service sending any packets?
You need to trace step by step what's going on - run the agent, initiate requests etc and at each stage looking via wireshark to see what is (or isn't) being sent/received. Obviously set filters for snmp packets only to avoid being swamped with captures.
So the requests are being generated by the agent, they are getting through to the snmp service and the snmp service is responding. Either the response is being blocked by a firewall or it is not being reported by the agent. If you've tried more than one agent it seems most likely that the reply packets are being blocked. Have you tried something like nmap to confirm ports open along the entire service/agent route:
Your issue may be that windows 7 as default only allows snmp quiries from the localhost. To enable network snmp request create a shortcut to services.msc and right click this short cut and select run as administrator - to ensure you have sufficient access rights to make changes.
Scroll down the list to SNMP services <right Click> and select PROPERTIES.
In the service properites click on the Security Tab
and Add the IP of your monitoring computer.
This will enable remote monitoring of the SNMP You might also need to configure community names.