I have 3 computers connected via ethernet cable all running to a router in my garage which is hooked up to a cable modem. I also have a laptop which has a built in wireless connection and connects to the wireless signal created by an access point. The access point is given its signal from an ethernet cable which also runs into the garage. All of the computers I am trying to network run Windows XP. I am trying to set up a home network with file sharing, the computers have different names, they are all in the same workgroup, but whenever I go to see the other workgroup computers, I either can't see the other computers, or I get an error that says I don't have access to that resource and that the path cannot be found. I'm pretty sure I get this problem because I can't ping any of the other computers from any computer. Please tell me how to fix this problem. Thanks in advance.

Install sp2 if you already havent. Make sure all your accounts in your computer are administrators. I would also reconfigure the router. I had this problem once, expect I was using Suse linux, anyway, try that and post back your results.

Good observation; if you can't even ping between machines, you're obviously going to have problems with higher-level sharing functions.

Can all of the computers access the Internet without issue (proving that your basic TCP/IP settings are correct)?

When troubleshooting any network-related issue, the first thing you need to do is to completely disable any firewall software (including XP's built-in ICF/ICS features). Simply choosing the "Disable" option in the firewall program's settings/preferences rarely turns the firewall off entirely; you will need to deselect the preference setting that tells the firewall to automatically start when Windows boots, and then restart the computers. After reboot, verify that the firewall is indeed disabled.
Keep your firewalls dropped until you get things working.

Once you've addressed the firewall issue, see if you can now ping between all machines. If not, post the exact error(s) returned by the pings.