sbs 2011 no internet access when plugged into switch

This is puzzling me....We have a small SBS 2011 network, modem/router - fixed IP, DHCP disabled, patch lead to switch. Networked PCs to switch, SBS box patched to switch - SBS: DNS server, DHCP server - all was working fine until this weekend. ISP had some service issues - Monday morning network was erratic - router light eventually showing internet connection but clients had intermittent connectivity both to server and internet.
Nothing particular showing in logs. Ran fix my network - couldn't find router. Ran troubleshooter and reported DNS unresponsive. Started to swap out items - replaced router - worked for a while, installed new NIC, swapped out switch, replaced patch leads. The only way that I can get clients onto domain and internet (ad working efficiently)  is using the ports on the router - as soon as I introduce the switch, internet goes, server connectivity goes. I have tried to re run internet wizard - it doesn't find the router but if I manually input the IP addresses of the server and router it works.
I need the additional ports that the switch provides (and this all worked quite happily for 6 months before this weekend). Should I remove the DNS and DHCP services and reinstall these services?

Any guidance would be massively appreciated
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If you don't mind me asking but what Switch and router is in play here?
jad2009Author Commented:
the router is a netgear n600 and the switch is a managed netgear gigabyte switch
The issue looks like it might be at the switch side as when you remove it connectivity is good, have you tried getting a warranty swapout on the switch? You couls try reinstall the services but i dont see how that could help the situation.
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Server - switch - router

jad2009Author Commented:
yes - generally server and clients into switch, then switch into router. Have already swapped out router for a new one - same issues. The only way to make the network function is to use the 4 ports on the router - as soon as I introduce the switch, network connectivity issues
What switch do you have specifically?
jad2009Author Commented:
The original one was a Netgear ProSafe 16 Port Gigabit Ethernet Switch JGS516-20
I swapped it out with an 8 port unmanaged - same issue with both switches
jad2009Author Commented:
I have just been back to the site to confirm the situation again - the new switch is autosensing. With the server and 2 clients plugged into the router - all works fine. If I connect the router and the switch - the switch has green lights but the connecting port at the router is orange - I have tried several different patch leads - all report the same.

Have the switch connected to the router and disconnect your clients one by one to see if that helps narrow down if the issue is being caused by one your clients (Servers/PCs) it may even be an issue where something is broadcasting a lot of network traffic hence causing this issue.

Have you re-installed the DHCP services? Are you sure the router/switch (Managed Switch) isn't trying to handle the DHCP requests as well as your DHCP server?

I'm beginning to think the issue might with one of your clients rather than the networking devices. Try the above and come back to me.

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jad2009Author Commented:
I'm back on site on Friday - I will reinstall DHCP - it is def off on router. I'll get back to you. Thank you
jad2009Author Commented:
Back to site today - removed everything from switch and one by one added each device back in and tested at each stage. The last device to be plugged in: an old router serving as a wireless access point - bang! No internet and screwed up DNS. Removed everything - restarted server. Added all devices again but binned the WAP - all stable and functioning. Thank you RoshanEjaz for your support and advice
BOOM! job done my friend :)
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