HP 2920 with 2 VLANs Problem while downloading

[Alternative]

Hi

I have a 2920 with two VLAN one for the datas and another one for voices.

As soon as I wan't to download something, for example Windows Update, network collapse and I lost pings (timeout)  while pinging the internet and responses times are very bad.

I have no QoS enable but 

If I have only the default VLAN for data  I have no problem... accessing the web with the other computers is not a problem.

I wanted to test after I enable : qos type-of-service diff-services but I don't even know if it is the way..

I don't know what to do... If somebody have an idea.

Thanks !

[Vince-Whirlwind]

We need to see the switch config, and make sure you have added Descriptions to all the important switchports.