Windows – Access C$ drive of a PC from another PC within a local network

I just reinstalled windows on my laptop and PC and found that I can no longer access laptop drives from the PC by going to e.g. \\MyLaptop\c$

I used to be able to do this, but now I'm getting an error.

Here's the details of the current state:

• I can see MyLaptop from MyPC under Network.
• When I click MyLaptop and I can see a shared Users folder.
• When I try to open \\MyLaptop\C$ I get a login box, but when I enter the credentials (using MyLaptop\LaptopUser format) I get a message: MyLaptop is not accessible. You might not have permissions… (before I was also getting 'access denied').
• The LaptopUser is the main user (administrator) on MyLaptop and I used to be able to access the drives this way before. It is also added to Security tab of the drive with Full control permissions.
• Both devices are using the same wifi connection and both are in the same homegroup (not sure if I need it though, I don't remember using it previously).
• Both devices are using Windows 7 (same as before the reinstall).
• MyLaptop is on Win7 Home Premium, MyPC is on Win7 Professional.

I know I can share the C drive (or any other drive/folder), but I would prefer not to do this, I know I didn't have to do this before.

Any advice would be appreciated.

Update:

After un-sharing the Users folder on both devices the homegroup now shows no other homegroup computers available, but both computers are still visible under Network. Trying to access the C$ drive of one from another now still shows the login box, but logging in results in Access denied error message.

New Facts:

• After executing net user administrator /active:yes and setting password for administrator user I can now access the remote drive using that user's credentials. It works both ways with the administrator users for laptop and PC.
• Therefore my question now is – what is the difference between the built-in administrator account and the non-built-in LaptopUser/PCUser account, which are also administrator type users?, ideally I would like to be able to do this using LaptopUser/PCUser