Similar to Jeff's but with more detail...
If your db is not secured and you are not using a runtime, then try this...
"C:\Program Files\Microsoft Office\Office\MSACCESS.EXE" "C:\Databases\YourDB.mdb"
If your db is secured with a workgroup, then try this...
"C:\Program Files\Microsoft Office\Office\MSACCESS.EXE" /wrkgrp "C:\Databases\YourWorkGroupFile.mdw" "C:\Databases\YourDB.mdb" /user TestUser
If your db is secured with a workgroup and you are opening in runtime, then try this...
"C:\Program Files\Microsoft Office\Office\MSACCESS.EXE" /runtime /wrkgrp "C:\Databases\YourWorkGroupFile.mdw" "C:\Databases\YourDB.mdb" /user TestUser