The shut down problem is probably because the hijacker is NOT completely removed.
They often leave links in services and the registry that DONT get removed by the anti-malware programs.
If you need assistance a Hijackthis log would show any problems. Post a HJT log here can be a problem - the boards software is not very helpful - you can post on any of these forum click here for assistance (or mine that is not yet a member click here although I am personally.)
Hijackthis is available from click here
Proud Member of ASAP click here