Start first to configure the HP switch A5120 to do this you need to connect your computer with a console cable to the switch. And enter the system–view mode.

To rename the switch name you can use the command sysname

To configure an IP address on the default VLAN interface. (VLAN 1) use the command interface
vlan–interface 1

Use the command quit to exit the interface setup.
To enable the http web interface

To enable telnet on the switch

Set an admin account for the switch

Set a line vty 0 4 password

Enter save to save the configuration.
To make a trunk on the A5120 switch

(Commands)
Trunk:
interface bridge-aggregation 1 link-aggregation mode dynamic quit interface GigabitEthernet 1/0/23 port link-aggregation group 1 quit interface GigabitEthernet 1/0/24 port link-aggregation group 1 quit interface bridge-aggregation 1 port link-type trunk port trunk permit vlan all
HP Procurve 2626 configuration.
To get the trunk working between the A5120 and the HP Procurve 2626 you need to do the following on the HP Procurve 2626 switch

Make a trunk on equal port speeds for example 1000Mbits (1Gb/s) configure these ports as an LACP trunk
To be sure configured first spanning-tree otherwise your switch hangs. And you can only do something on the console..