I have a wireless router upstairs...to far for wireless and too far for a cable. i had an old comcast modem that i hooked up to the cable outlet by our hdtv and comcast hdcable box...i have a 1 to 2 splitter...hooded one cable to the hd cablebox and the other to the modem...it worked for awhile until comcast blocked their old modem. they want $45/monthy to hook up the old modem. If i buy a new modem (that isnt from comcast) from best buy and hook it up with the splitter and ethernet cabel do you think it would work?
No, and then you'd be stealing cable. As much as i hate comcast, its not their fault that your router isnt strong enough to transmit to where you have your TV. The only reason the "old" modem worked at all is because at one point in time comcast had it registered in their system to your account, if you go and out and buy a brand new modem its just going to sit on your TV stand and blink because comcast has not activated it.
what is the distance from your router to your TV? What kind of router do you currently have? how much money are you willing to spend on new hardware in order to get this to work? Are you opposed to cutting holes in your wall and running Ethernet cable throughout the house?