SG300-28P switch stops working withmore than 1 device plugged in .

Hello all I have an issue with my SG300-28P switch. I am replacing a previous switch of the same type, I can plug in both Fiber gigabit ports and all the network and VOIP phones work just fine. I can then plug in one port connection and they still work fine, but the moment that I add 2 or more connections to the switch it drops the network from the VOIP phones and PC's. Oddly the phones stay lit up and on but no dial tone comes through.

Network is Windows 2008R2
Phones are Panasonic KX-NT343
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NetExpert Network Solutions Pte LtdTechnical SpecialistCommented:
@    BSAS_ITGuy, can you paste the running config of the  SG300-28P switch and let me know , what device you connecting to the switch and in what port number

If you connect a network device into the switch and if the new device can support STP, then there might be loop can cause outage in network.


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