The Internet is disconnected, what should I do?

Question

Computer networks

Good afternoon.
The situation is as follows: everything was fine, then the "masters" came to change and reconfigure the cash registers + put a router-2 instead of a switch). After that, problems with the Internet appeared on PC-2 and PC-3: either the Internet is working (it lasts 5-10 seconds, pages are loaded at maximum speed), or there is no Internet at all (20-30 seconds). You have to press f5 many, many times in order not to miss the chance to get to the right page, download a file that weighs more than 30mb, there is no chance at all (the download is interrupted). The internet icon does not disappear. There are no problems on PC-1.
The brave guys have been promising to come for 2 weeks, but, apparently, this will not happen, I ask you for help.

Answer 1

Check if DHCP servers are accidentally configured on two routers at once?
It is possible that they issue addresses from the same range. Separate the ranges.

Answer 2

Do router 1 and 2 IP do not intersect?

Answer 3

Write router models