got internet connections but browsers fail to open

sorting a pc out for my cousin
he has internet connection as i can up date his anti virus etc no problem

but when he trys to lauch IE or google chrome its goes to lanch then closes traight away, even tried install chrome again from the exe. file but it does the same.Chrome also seems to have disappered from the list in programs.Run a full virus scan after updating AV zone alrams and it finds nothing

any suggestions please

runing vista home edition 32 bit

You may want to test with a clean boot
Troubleshoot Application Conflicts by Performing a Clean Startup - Windows 7 Forums
If that does not work, test with anti virus and firewall turned off. Turn them back on qucikly to avoid possible infection.