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Thank you for asking this question in the Support Community. You will have to setup UDP relay to forward DHCP Discovery messages to a DHCP server on another subnet. Many services, such as DHCP, rely on clients being able to reach a server by broadcasting a request. These requests are limited by being broadcast. Broadcast traffic propagates only throughout the local subnet. If the client is not on the same subnet as the server, the broadcast will not reach the server. If it is necessary for clients to have the ability to communicate with a remote server through broadcast traffic, then UDP Relay must be enabled. UDP Relay, once set up, will not simply forward the broadcast packets. It also examines them, checks their validity, and adds any appropriate changes, such as its own IP address (which enables the server to return the traffic to the router). The router will then forward this traffic to the client. Here is the Configuring UDP Relay in AOS guide for your reference.
In your configuration, you will need to point the ip helper-address to the DHCP server's IP address, not the VLAN IP address. So, the command would be ip helper-address 192.168.5.2 on both VLAN 3 and 4 since the DHCP server will be 192.168.5.2. You will need to enable UDP relay for DHCP with the ip forward-protocol udp bootps and ip forward-protocol udp domain commands.
Also, the commands switchport nonegotiate and spanning-tree portfast you mentioned above are not AOS commands and will not be accepted. If your intention is to hardset the speed/duplex to 100 Mbps then the command is speed 100. Also, typically the port connecting to the DHCP server would not need to be setup as a trunk port in this configuration.
Here is an example configuration based on the information you provided:
ip forward-protocol udp domain
ip forward-protocol udp bootps
interface switchport 0/10
description Trunk_2_DHCP_Server
speed 100
spanning-tree edgeport
no shutdown
switchport access vlan 5
interface vlan 3
description 3rd_Floor
ip address 192.168.3.1 255.255.255.0
ip helper-address 192.168.5.2
ip route-cache express
no shutdown
!
interface vlan 4
descrition 4th_Floor
ip address 192.168.4.1 255.255.255.0
ip helper-address 192.168.5.2
no ip route-cache express
no shutdown
I hope that makes sense, but please do not hesitate to reply to this post with any additional information or questions. I will be happy to help in any way I can.
Levi
