system
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bri,
This does not sound like a browser hijack to me.
It appears to be a proxy conflict. If the browser was hijacked, then surely it would not default to where the user has it set. You said this is not the case.
In addition, when you remove the system from proxy configuration, it works fine.
Firstly, in the Internet Options above where you enter proxy data, if the box Automatic detection is checked, that would explain why it defaults to proxy settings on a reboot.
I think you need to check into such things as firewall settings, antivirus configuration etc.