Part of the problem is that you are giving nearly useless information.  Take your time answering our questions and we will be better able to help you.  I do not believe reinstalling Windows is neccisary, this is generally the desperate attempt of someone who doesnt understand what they are dealing with.  Think carefully, explain completly, listen closely and we can probably help you solve this problem without a reinstall of windows.
If you are able to ping one machine from the other but not vice versa please list the following information for us for each machine:
how are the IP addresses set, statically or are they assigned from a dhcp server?
do an ipconfig /all and give us:
Ip address
subnet mask
gateway
dns server(s)
computer name
workgroup name
after getting that information we will proceed.