1) Check alfresco-virtserver.property file in \virtual-tomcat\conf\
alfresco.server.password = xxx (here give the password, which you had it during installation)
2)Not sue about this. But I had problem only in this point..
Installed location of our alfresco community is also considered here. If it is installed inside any folders, eg say- Program Files or Document and settings, the space between them creates an error (Program%2DFiles). So after installing it in C:\ Alfresco\, it avoided some startup errors..
I hope you would be corrected with the 2nd point..