At the moment, I use a TV connected via RGB cable as my monitor and it works ok (with the slight exception of sometimes not turning on when I wake up the PC). Now I wish to change my PC to "monitor" conection from RGB to HDMI but when I switch to the HDMI connection My fences and taskbar don't show at all. Any help would be appreciated.

What's the resolution of the TV and what's the resolution set on the computer?

You also may need to change the aspect ratio in the TV settings. Some of them don't display things from a computer properly even though both are set to the right resolutions and all and need to change the aspect ratio.

Gonna have to do lots of fiddling with your resolution it sounds like. TVs are notorious for having really wonky native resolutions and overscan areas, especially older TVs. If the TV has a "PC mode" enable that too.