I just got a service replacement [48G+] from HP and I transferred some programs to my 48G+. Problem is after using it for a couple of minutes, it started to go crazy, the screen looked as if part was working and part was not, a set of lines came up on half of the screen and then it just went blank.

You should post this question on the comp.sys.hp48 newsgroup. The experts are all there and they are very friendly. It sounds like a library issue, or a hard failure. If you still have the manual you should find out about doing a "hard" reset. This will erase all your downloaded files, but it should bring the machine back. It is usually done by holding down a key or sequence of keys while turning the machine on. The guys on that news group can help you.