Can't find PC in a Workgroup

Hi, I have maybe a stupid question but I'am still learning and I just wonder what can I do to sort this problem out. In my office I have:
4 PC`s on WinXP SP3, all connect using wireless network. On 3 PC's there is installed only the software(no database) that i need for my job. On 4th PC we have installed software and all database( to which we are connecting from our 3 PC's to obtain all information to use our programs correctly). And everything was working fine we used one router whic connected all 4 PC's and printers to internet and we shared all details with no problems. But then we moved the PC4 to room next to my office. So what we done is: all PC's( 1,2,3) in my office still connect using the same Router(1). In the room next to my office we installed new cable router(2) and we connected this router(2) to the router(1). The internet works fine on PC4 in this room, we still can use printer in the office but none of other PC's 1,2,3 don't have any acess to database on PC4 like before. All firewalls been disables and antiviruses on all PC's but I can't see PC4 on my workgroup anymore i created new network but still couldn't find the PC4. I ping ip adress from PC4 to any of the PC's1,2,3 in the office and its connecting with no problems but I can't ping PC4 from any PC from the office. I disabled the firewall in the Router(2) What else can I do as I said before I am still learning

Thanks

 

It’d really be easier to use a switch instead of a router. Plug it in and you’re done.

Anyway.
Sounds like wiring.
Do NOT use the WAN port on router (2). Use a regular port on (2) to regular port on (1).

If that's already done then an IP problem.
You’re using router(2) as a switch so disable everything on it.
Disable DHCP to avoid conflicts with (1).
Make sure it and the computer are in the same range as (1): 192.168.1.XXX – (whatever 1st 3 numbers router (1) uses).
You’ll probably have to use static addresses on router(2) and PC4

 

I did all this changes. Now I am able to see every pc in my workgroup. Thanks for you help