What happens is prolly that the serverlisting takes memory or bandwidth which slows frames etc.
Are you sure it locks up, not just collecting info before it gets on screen?
Try a smaller listing like last man standing, less servers might not lock up, and wait a little longer
Or choose an adress of a known server and type it in the adress window, if this orks, you kow you at leats can get connected
If not, and the problem is UT related then maybe:
Look at this snippet from my unrealtournament.ini
Enable allowdownloads
Try fiddling with the numbers, you can change them on the fly under network tcp/ip in prefernces menu
Let UT run in a window, by resizing the UT window, then experiment
[IpDrv.TcpNetDriver]
AllowDownloads=True
ConnectionTimeout=15.000000
InitialConnectTimeout=300.000000
AckTimeout=1.0
KeepAliveTime=0.200000
MaxClientRate=3500
SimLatency=0
RelevantTimeout=5.000000
SpawnPrioritySeconds=1.000000
ServerTravelPause=4.000000
NetServerMaxTickRate=20
LanServerMaxTickRate=35
OverrideBufferAllocation=False
MaxDownloadSize=0
DownloadManagers=IpDrv.HTTPDownload
DownloadManagers=Engine.ChannelDownload