BleepingComputer.com: Can't see other computers connected to network

Hey guys
I'm having some trouble connecting to other computers on my network... basically I cant see any of them. :S
I've tried with 3 diffrent computers...
Computer 1: Can't ping either Computer 2 or Computer 3 (Running Windows 7)
Computer 2: Can ping Computer 1 but not Computer 3 (Running XP)
Computer 3: Can ping Computer 1 but not Computer 2 (Running XP)

When I try to connect to Computer 1 using Computer 2/3 (\\ IP adress), it asks me for a user name and password... which user and pass does this mean?

Also, when I search for other computers on the network, I can't see any.

Does anyone have any advice?

Thanks in advance.

all computers have to belong to the same workgroup, that is something that you can check. also i suggest you turn off all firewalls until you get the computers to see one another. once you have your network up and running then you can turn your firewalls back on.

Computers 2 and 3 are asking for username and password of Computer 1.
But Computer 1 is Windows 7. If it were XP, wide open XP, it wouldn't ask, because, at least on the Home version it's all under the GUEST account.

But Windows7, I suspect, works differently. If it has good security as people claim it does, you may need to, in Windows7, somehow permit the users of Computers 2 and 3, as well as, of course, having setup few folders where you permit other computers to work them. Pinging included.

I now see that you have issues with XP as well. Follow caperdog's suggestion to try without the firewalls, same workgroups, some folders to permit sharing, reboot if needed, as this sometimes may help.

Do all these computers have different IP addresses? The more I reread the questions, the more it looks like some basic setup is not yet finished. For instance, are all these wired connections? If not, is the router setup properly to permit all the MAC addresses in the security section?

I am going to assume a couple thing, PLEASE let me know if I am incorrect on anything: you have all 3 connected to the same router? you can surf the net with all 3? you have enabled File/Printer sharing on all 3? they are all in the same workgroup(Windows 7's HomeGroup thing will not work with XP so you can't use it)?

The first 2 things I assumed have to do with pinging. Now either there is something amiss with the IP addresses of the 3 PCs OR you have firewalls on. My advice would be to turn off any and all firewalls. If all 3 are connected to the same router, make sure if you have static IP addresses that they are in the same network.

When it comes to sharing, make sure you have something shared on each PC. I have a Virtual Machine that I installed Win7. I did it to see what it was like and its like I thought it would be lol. The first post here has the best step by step for Win7 on how to set it up. The permissions thing, step 4, should be done on all 3 machines. Just to make sure.

I'm pretty sure all computers are in the workgroup: "WORKGROUP".
I tried turning off firewalls, didn't work...
Is the router setup properly to permit all the MAC addresses in the security section? Umm... I'm not sure what you mean :S Could you explain more?

does windows 7 have a network set up wizard ? if so try using that