Cisco 3750 initialization drops network connectivity

Experienced the same problems, when for some peculiar reasen I had connected some pc's directly to a 2924 switch. The pc's never got an IP adress because the DHCP request timed out, before the STP "settled". I think the only reason is to disable STP on the switch ( I don't think it can be done on a port base).

3 Cisco 3750 switches connected together.When any RJ45 gets plugged in or out, the switch re-initializes for 10-15 secs, thus dumping every device off the network momentarily. The LED's flash orange during this time, then go back to green (normal)

I assume that it may be spanning tree protocol related, but how can I stop this from happening. Even if I poweroff/restart a server that is connected to the switch, we lose connections to the network.

Any ideas on how to resolve this problem.

Thanks