I believe he's on the same LAN. The problem is that STP is putting the ports on the 2924 in blocking mode when the PC's first power up, and given that they probably power up very fast, the port doesn't go into forwarding mode when the DHCP request tries to go out, and thus the problem. Two solutions are to shorten the STP port blocking to fowarding delay, or remove it completely (just don't patch your switches in a loop, or don't set this last config on any ports that will not be directly connected to an end node). This first line will configure your switch to only wait 15 seconds before going from blocking to forwarding mode (should be adequate for STP to work, but PCs to boot and have DHCP or whatever else work):
spanning-tree vlan 1 forward-time 15
Worst case, just nuke the delay altogether (I've done this for some ultra-fast booting PCs that boot in DOS first, check the network for config changes, then continue booting normally). What this will do is disable the default wait time between blocking and forwarding on the ports when they first come up:
interface FastEthernet0/1
spanning-tree portfast
!
interface FastEthernet0/2
spanning-tree portfast
!
interface FastEthernet0/3
spanning-tree portfast
!
interface FastEthernet0/4
spanning-tree portfast
!
interface FastEthernet0/5
spanning-tree portfast
!
interface FastEthernet0/6
spanning-tree portfast
!
interface FastEthernet0/7
spanning-tree portfast
!
interface FastEthernet0/8
spanning-tree portfast
!
interface FastEthernet0/9
spanning-tree portfast
!
interface FastEthernet0/10
spanning-tree portfast
!
interface FastEthernet0/11
spanning-tree portfast
!
interface FastEthernet0/12
spanning-tree portfast
!
interface FastEthernet0/13
spanning-tree portfast
!
interface FastEthernet0/14
spanning-tree portfast
!
interface FastEthernet0/15
spanning-tree portfast
!
interface FastEthernet0/16
spanning-tree portfast
!
interface FastEthernet0/17
spanning-tree portfast
!
interface FastEthernet0/18
spanning-tree portfast
!
interface FastEthernet0/19
spanning-tree portfast
!
interface FastEthernet0/20
spanning-tree portfast
!
interface FastEthernet0/21
spanning-tree portfast
!
interface FastEthernet0/22
spanning-tree portfast
!
interface FastEthernet0/23
spanning-tree portfast
!
interface FastEthernet0/24
spanning-tree portfast
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