I believe most desktop PCs from the past few years can run this pack. You just need to allocate 2 GB of RAM. You need Java 64 bit to do this. If you have that already, use the cog wheel on the Technic Launcher screen to allocate more RAM.
I can think of three reasons.
A. Your internet isn't good enough to connect to a server
B. The server is too far away to connect to. (You might be in the US, but the server is in the UK; or visa versa.)
C. You miss-typed the server address.
I'm not sure, but I think this should go either in the Tracker or the Platform Pagoda. I know the tracker is for sure, but since you added a mod, it should go in the PP forum.