Thank you,skyliner,for trying to help me.

Here are some of my system details:
1.Windows XP Professional with SP 2
2.Norton Internet Security Online 2008 personal Firewire
3.DDDRAMM-007 = DIM PC3200 - 512MB DDR x 2 = 1024MB
4.Available space on C: = 78,1GB
5.Broadband ( ADSL )
6.Alcatel Speed Touch USB-modem
7.Appartment complex
8.LimeWire 4.16.7
Java 1.5.0
9.ISP = Belgacom Internet Provider
10.Test worked
11.No
12.New problem
13.Yes
14.UPnP enabled
15.Norton Internet Security Online 2008
16.Belgium

I didn't change anything on the system but now, out of the blue,I have sometimes immediately contact with LimeWire ( the brick wall is gone )
and sometimes there is no contact (???).

Yours sincerely,
Willy