Cant Access \\Computername\c$

Mizraab

I am unable to access my hard disk from my Laptop but i can access my
Laptop's hard disk from my desktop pc :S
I am putting correct username and password but its still not working.
please help

My desktop is running on Windows Xp
My Laptop is running on Windows Vista

I can access my shared files/folders using \\computername but i cant access
my hard disk using \\computername\c$ command.