You don't say which PC is inaccessible but I assume it is XP *PRO*. Normally to access XP Pro, you have to be logged in to the 'client' PC with a Username and Password that matches an Account set up in XP Pro. For more on this, see click here
<<< The host cannot access the client Machine even though Hdd enabled as shared >>>
It is not generally a good idea to share the root of the drive, you should share the folders that you want to have available over the network. The files on "C" drive don't all belong to you, i.e. they don't all belong to the User Account with which you are logged on and this can cause problems if you simply "share" the entire drive.