Computer shuts down unexpectedly only when on the internet

[sierrarscosworth]

hi!! i'm new!! i have a problem with my compaq presario 2135EU. Any time i am on the internet the computer shuts down unexpectedly only when on the internet.
i have installed windows again 6 times but with no luck. it uses a usb modem.
the modem is a Thomson speedtouch 330. i have updated the computer and tried looking for an update for my modem but to no avail. Please Help!!!!

 

[holdenssx]

Have you tried using different internet browsers?

 

[Punk]

Have you scanned your computer with an anti-virus software?

 

[sierrarscosworth]

tried mozilla firefox and scanned for malware and viruses. also turns off when downloading updates with no internet page