Network traffic Problems - Please help URGENT

You can use Cacti for snmp monitoring of your switches,
if your switches are managed -  they might have basic monitoring built in, or at least you can check the logs for errors, exessive broadcasts...

As you have mentioned that at about 14:10 you face this issue, is it possible for you to check if any kind of updates are happening internally, like Antivirus update, MS update etc.

Sorry No, it's not updates ... the whole network locks down solid. I'm sure there's one rogue machine but I cant find it!
Thanks evgeny_f21, I'll look into it right away. How does it differ from WireShark (I dont know either)..?

If your switches are locking up due to some activity on the network, I would be willing to bet that you're seeing excessive broadcast traffic.  If that is the case, setting up a machine with Wireshark on it should allow you to pinpoint the source of the traffic, and may not require any special configuration of your switches.

If the problem is not caused by broadcast traffic but is still caused by traffic of some sort, you should still be able to capture it with wireshark and analyze it but it gets somewhat more involved.  In that case, it's important to make the distinction between switches and hubs.

If you're sure you have switches and NOT hubs, you will have to configure at least one of the switches with a "monitor port", which re-broadcasts all of the switch traffic out that port so it can be captured with a packet sniffer.  This requires a managed switch - if your switches are unmanaged, you're out of luck with this approach.

However, if you do have hubs and not switches then the first approach I suggested should work, as hubs broadcast all incoming traffic out all ports, which in a network like yours could cause so many collisions that it simply stops the network.

Thanks BasementCat, that's exactly what I've been thinking. I also  thinki it's broadcast. The switches are some 3COM Managed switches, and they have their own little interface. I installed Cacti as suggested by evgeny_f31 but can't seem to get it to recognize the switches. They are 3Com Baseline Switch 2928-SFP Plus Software Version Release 1101P10.
Unfortunately I know very little about network analysis, I've always been on the software analysis/development and hardware for fun side!

I am quite willing to let you connect to the wireshark machine or even to the switches web management .

fdl333, I have actually done this on 3com switches before - it's really quite easy to set up.  If the traffic that is being a problem is actually broadcast traffic, then all you need to do is run wireshark on any machine that is directly connected to a switch that is affected by this problem.  To create a network traffic dump for others to analyze:
Do this sometime before you usually see that burst in traffic, and you can stop wireshark once it has gone on for a little while, all you have to do is close the program and confirm if it asks you to save the capture file.  Once you have the capture file, anyone with a copy of wireshark can open it and analyze it.  If you'd like to do a capture I'd be happy to analyze it for you.

BasementCat you're a real angel !
I'll do exactly that today (european time)
Thanks and speak soon..
I played with wireshark yesterday and I noticed that one of my ADSL routers sends about 70 "who is xxx.xxx.xx.xxx. reply to (it's own ip add)" is this normal?

Thanks BasementCat!
I put it on our website 'cause it's 64M and I don't think I can u/l it here
http://www.timoholding.com/fdl/SharkForBasementCat.rar
IF you see a lot of traffic from 192.0.0.23 it's my pc downloading from Giganews ...

Sort this one out and you'll definetly get all the points!

Here's what I'm seeing so far:  initially, you're getting a huge flood of packets with the TCP reset flag set from 195.22.200.178:80 to 192.0.1.22 on either port 50126 or 50128, but I don't think that this is the source of your problem - it only seems to occur once.  Next, I'm seeing a flood of ARP requests (several million of them, around 10,000 per second) for 192.0.1.57 and 192.0.1.86 from either 192.0.0.64 (20:fd:f1:08:98:5c) or 192.0.0.66 (20:fd:f1:08:7f:86), this makes up most of that packet capture.  Those mac address ranges seem to belong to 3com europe - I would start by tracking down the devices that have those mac addresses, or those IPs, starting with any 3com equipment.

Yep, last night I captured an enormous file of
"who has (ipaddres) tell (address of two of the 3com switches)"
It stopped when I rebooted one of our routers.
But it's really odd, 'cause we bought the three 3coms (ip's .64, .65 and .66) to try to solve the problem!
Why is there so much "who as xxxx" ARP traffic? II don't understand networking at this level, but it looks like an attack from outside to me

You have ALL been very helpful. Just one last thing. Can anyone tell me HOW to configure Cactii tfor the 3 com switches. They are 3Com Baseline Switch 2928-SFP Plus Software Version Release 1101P10.

http://www.cacti.net/documentation.php