I got a few HD digital cable channels..but now they are scrambled?

hi, i never upgraded to digital...i have straight og cable. but i recently got a hdtv and noticed that i got a few digital channels (fox, cw, wmht). now when i go to the digital channel it says weak or no signal. i only have the standard channels now. did they notice this and block the channels or was it just a freak thing?? thanks