Re-running the network setup disk was the what caused problem with your shared files.(re-share) Re-set the share this file setting of the files you can't see. You could also try system restore on your first two PC's, if no date prior to the 3rd computers system add date, restore is not an option.
The 3rd PC is it Home or Pro? Pro XP has a problem with peer to peer networks. Wireless complicates the matter. Do you use a router or is it an adhoc wireless Network?
There are several reasons possible for this, but the printer access clears up some of them. Is it part of the MSHOME network or is it WORKGROUP network? This is an XP pro issue. Home XP is MSHOME and Pro is WORKGROUP. This caused me the same problem. if this doesn't solve the problem, please post more on the wireless setup and Xp pro of home?
I have a 2wire gateway on a desktop PC, a wireless notebook and a 2nd desktop with a linkys wireless adapter. All XP machines. My problem is file sharing. The 1st PC and laptop were OK initially, I added the 3rd wireless desktop and it can access the shared printers of the first 2 - but they can't access the new PC.
Then all 3 couldn't share at all - so I reran the nework setup and made sure the firewall is defaulted off. Now 1 & 2 can read the original Windows shared file of each machine, but not my files I have set as shared in both. Also they still can't reach the 3rd desktop at all - same error message says I ''don't have the rights to access - see admin' for both scenarios.
Frustrated - help?

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