Unable to view my other Macs over network

Hello all ..., I need some help here.

I have 3 computers. MacPro, Macbook Pro, G5 PPC.

I often work from home and need access to my files at my office.

Up until a while ago (I think around the time I switched my internet provider from one service to AT&T Uverse) I was able to open my laptop and see my MacPro (back at my office) in my list of available network drives in a Finder window.

Since the switch, I'm unable to access my off-site computers.

All my computers are running 10.6.8.

I have been doing some research on this and have read plenty of people who are still on 10.6.8 being able to still access their computers remotely.

I also came across some sites that suggest that my issue is at home, where my new modem and ISP were installed, with some sort of firewall or porting issue.

I realize MobileMe is discontinued so accessing "Back to My Mac" isn't available on my laptop due to, at some point, my MobileMe account got signed out in my system prefs on my Laptop and I'm not able to sign back in to access the "Back To My Mac" prefs.

If other people are still able to remotely access the computers who are still using 10.6.8, why can't I?

Has anyone ran into this issue?

I do have parallels installed on all computers and my mobile devices but using the iPad and iPhone to access and control my office computers is VERY cumbersome and not quick enough.

A while ago I was in Vegas and was able to screen share my computers and it worked beautifully. Wondering what, if anything, I can do to resolve this.

Responses of "update everything to Mountain Lion" isn't an option for me at the moment as my Laptop is an older laptop and won't accept ML. And, due to programs not being compatible, I can't afford to update to ML and lose those applications.

any help is appreciated!!!