Two Dell Computers - Unable To Share Folders

i have 2 dell computers (and more but just worried about these two for now)... mainpc and sparepc, i had sparepc hooked to my tv and all pc's in the house, and a tv, networked to it... it all worked great, after a few minutes of setting it up... and then the hard drive crashed on spare pc and i got a new one, installed windows again both pc's use the same installation disk both pc's are hooked to a workswitch, which is hooked to a uverse gateway (router)... but it should be noted that hooking everything to wireless changes nothing... i get the same results can reach out to anything in the house and network great... but nothing can connect to sparepc... it keeps asking for username/password, even tho none is set I've gone through all the file sharing, homegroup, and folder options... ive reset ownership on folders and permissions... ive tried making/changing user profiles... but i cannot get from mainpc to sparepc home group does not work because the network does not work. as soon as the network works, homegroup will spring to life (at least, thats what happened the last time) if i right click on a folder, go to properties, share tab, and hit the share button... it asks for permissions for users... i set them, hit share, and it comes up and says, "you cant share this folder" ... with no explanation