Thanks to all who has given idea.
Will try the simplest first, and try IPA and clean it.
If that doesn't work I will try to resolder the cpu.
I really don't want to send it back, as Canada is very far away
Didn't know it was supposed to click in place without screws, as mine is very loose(or I'm not pressing it hard enough on).
Turran: I also have an 8mb board for a different A600. This is detected, but must use the screws or contact is lost. So looks like the same problem.