File sharing

I have just been perfecting my networking, and have been able to sort one machine (AMD), on my network to share files and folders.  The second machine which is known as (P4) on my network, is able to be seen in the workgroup, but not accessable.  This may be due to users playing with the services.msc. Is there a way to change these settings back to default?.
When you browse my network places you see shared folders of the amd right away, but nothing shows for the folders of the P4.  Also when you access the P4 is says unorthorised "dont have rights".

Additional information:

1 x wireless router

P4 connected hard wire to router, and AMD is connected via wireless 802.11g+ to the wireless router of which the P4 is connected.

Internet access is also shared through the same router, which windows says may cause conflict, or security breach if sharing files and folders on same connection.  Which i want to do, and already have configured correctly.

Diagnose/troubleshooting:

I have ran the network setup wizard and choose other connection to share files and folders and DSL through 1 router.  Gave me the warnings of potential sec urity risks, so i disabled firewall on the connection and no joy.

Think my services.msc has been messed with on the P4.

This may be due to users playing with the services.msc. Is there a way to change these settings back to default?.

I suggest you refer to this list in order to manually reset service.msc to its default values.