network slow: 3 switches between router and pc

Well, a router might help to drive another media type - but probably not in this case, unless you are going to use some other technology for the longer distance.

Better approach would be to migrate the longer distance links to some inexpensive fiber some Multi Mode Fiber does drive GbE over up to 1000 meters or 10GbE on up to 550 meters.

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daniel-germany wrote:

looks like i can not extend the 100m limit with switches.

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Of course you can. However, for Ethernet the max reach is always 100 meters for 10/100/1000/1GBASE-T.  Using fiber much more. Your schema does not show an length exceeding 90 meters resp. 80 meters per hop, what would be fine. If there are 170 meters, the cabling and patching is not as per the drawing..

daniel-germany wrote:

The length of the cables and amount of switches caused packet collisions.

Of course, if the Ethernet links exceed 100 meters, troubles start on the link. For this you don't need Wireshark or any other rocket science. 

daniel-germany wrote:

The problem was solved by inserting routers.

Still don't see why a router. You want to build some continous L2 network, so why add routing along the ines is beyond me. Correct way to mitigate copper cable lengs > 100 meters would be the installtion of fiber. Alternate, you can add a L2 switch along the line..

On top of all that, it's a good rule when it comes to STP you should not exceed 7 hops for any connection, so the spanning-tree algorithm has enough time to converge.