Can't open new programs after first connect to internet

Dear all,

Please can you help me with the following problem.

I turn on my computer and then connect to the internet. If I try to
open any other programs I get the little hourglass for a couple of
seconds and then it goes, and the program does not load. Sometimes if
I wait long enough (in excess of 5 minutes) all the programs I have
been clicking on suddenly load altogether. Other times disconnecting
from the web, or pulling the cable out seems to allow the programs to
load (but that kindof defeats the object as I am then not online!).

This only happens when I am using my Tiscali broadband service and not
the LAN I have at work.

The details are:
1. Computer:
Acer TravelMate 292LCi
Intel Centrino Mobile Technology
Intel Pentium M 1.5GHz
Intel 855GM chipset
Intel PRO/Wireless 2200BG(802.11b/g WLAN)
15.0" XGA TFT LCD
40GB Ultra ATA/100 HDD
DVD/CD-RW combo drive
512MB DDR SDRAM

2. Software:
Windows XP professional
VirusScan Enterprise 8.0.0
Ad-Aware SE Personal
Spybot - Search & Destroy
a-squared StartCenter

3. Internet connection:
Tiscali Broadband
1Mps
Thomson 330 speedtouch USB modem ADSL PPP

I seen a few posts with similar problems but no solutions that have
worked for me. I have done full virus scans, run Ad-Aware, Spybot,
a-squared, and tried some registry cleaning programs, but the problems
remains (although my computer loads a lot quicker!). It does not seem
to happen the next time I connect.

Thank you for taking the time to read this, I look forward to any help,

Simon