Computer slows down when on the network

[A_Prime]

A user in the company I work at has a strange problem where the computer behaves very sluggishly when it is connected to the network.

 

The user is running Windows XP, when connected to the network, it will take 2-3 minutes to launch programs like Excel or Open Office. If I disable the network adapter, the program launches instantly.

 

I tried disabling the onboard NIC and installed a separate Intel Gigabit NIC in the PCI-E slot, same problem occurs.

 

Tried doing research on this topic and couldn't dig anything up.

 

Any input would be appreciated

 

            

[Sundanc3]

Maybe theres some malware that only is active when there is an active internet connection, and that is what is causing the slow down. 

[Sharif]

Maybe theres some malware that only is active when there is an active internet connection, and that is what is causing the slow down. 

try malware bytes