SPCR

After a new computer was installed, the LAN started to lose connection. The LAN configuration was as follows:
modem gateway -> switch1 -> switch2 -> PC1 (working)

After the new PC was installed, the LAN looked like this:
modem gateway-> switch1 -> switch2 -> PC1 and PC2 (lost connection)

When I took out one switch, the connection worked again with either switch:
modem gateway -> switch1 -> PC1 (working)
modem gateway -> switch2 -> PC1 (working)

But there are several rooms and I need the switches to connect devices. Could it be that my particular switch is not good enough to handle the complexity, and that a better switch will work?

In what way have they lost connection? If you use DHCP then you could instead try setting IP addresses manually (in the same range!) and see if it works then. That would possibly allow a workaround.

Are they actually switches, or just hubs? Switches should have no problems with your setup, but hubs might.

Did you actually try both PCs together with just one switch? Your diagram seems to show that you only tried one switch with one PC at a time.

Edit: Edh correctly points out that it could be a DHCP issue. How many devices do you have in total on your network? Your gateway may have run out of leases, some have very small default scopes.

Thanks for the replies. They lost connectivity to the internet. The DHCP range is large enough to accommodate the number of devices I have.

I may have fixed it: I noticed that the new computer (PC2 in my diagram) crashed and the OS became unstable and unusable. That computer has been having problems since I got it. After reinstalling the OS, I changed the switches back to the old configuration, and it worked again. Considering that the LAN had no such problems in the past, I think the likely culprit is the new computer overwhelming the network somehow, possibly bad ethernet driver installation.