I am able to ping a computer in the network but not able to access the share folder in the computer.
ICMP/Ping and shared drives have different access rules and settings on a host. By testing ICMP/Ping and getting a response from the host, you're only verifying the computer is responding to network calls (through the ICMP protocol). Now check your shared folder settings since these might not be setup properly. You should always include what Operating System when you have the question, also include your sharing method, as there are many methods of sharing folders.
Ah, Windows 2003...
Test the share from the same server \Name and see if this opens properly, also double check your folder share privileges to the user account trying to access the resource (shared folder). Another thing to try would be to check the server event logs and see if there are any errors pertaining to sharing or the server service.
One step up from PING is to see if you can get to the box via NetBIOS (over TCP/IP). My steps usually are:
nbtstat -A serverIP- if fail, check 135/139/445 (TCP) and 137/139 (UDP) open
nbtstat -a servername- if fail, check DNS/WINS is ok
net view \\servername
PortQueryUI can be used to check ports also. If ports are open, perhaps "can't access it" is really a security thing; check AD account ok, security messages in event logs.