Switch Failure

Hoping to replace my 10 mbps hubs with nice new 10/100 unmanaged switches, we ordered five 24 port Linksys switches. I shut down my network, stacked four of them, linked those four to a Cisco 2900 switch, and brought a small segment of the network back online to test (which succeeded). We loaded the first switch and had no problems. The minute we added anything to the second switch the whole thing stopped working. We worked with various trials and permutations (included removing the Cisco switch from the group) for a few hours with the same results - anytime we loaded anything onto more than one switch everything went down. I eventually ripped it all out and sent it back (especially after I called the vendor, looking for some information, and they tried to tell me they didn't make anything with that model #!), but I don't understand what went wrong. Any ideas?