IE6 unable to connect after Firefox uninstalled

I have windows XP.
I have unistalled firefox and IE6 is not working properly anymore.
The symtoms are the following:
At the start up IE6 connects to the basic page which is google.
From thereafter it is not able to connect to anything; if I write an address and go it displays a message saying that a "null" program is missing.
I can however connect through google, i.e. by searching through google i can select a site and connect.
Moreover IE6 cannot download anymore. No error message displayed.

Everything was functioning before, but the preferred browser was Firefox, and I did not changed that, before uninstalling Firefox.
A few guesses:
1.- In IE6 the preferring label is not present and perhaps it is not set. How can I restore it on the register?

2.- How can I reload or fix IE6? Since the original CD is not available, may I use another CD (genuine winddows XP) to copy files?

3.- I have searched for solutions and I have found IEFIX and setupxv.exe.
Who knows them?

Any help is highly appreciated.
best regards,

 

Thank you Petec,
I will try IEfix...