. . . . downloaded latest usb driver from internet for windows 8.1 . . . .
Unless you got the drivers from Magix it is likely that you have thewrong version of the drivers ie they are the 64 bit version, you need the 32 bit version of the drivers from here.
Once these are installed the program should work as normal.
Has the program worked before or is this the first time ?
When you play the video on the device you are trying to capture from, through the USB device, do you see this in the Preview screen?
RYVT 2 is an old version of the program which I do not have, however if you can see the video in the Preview screen and the Continue button is still blank, the program may be waiting for you to select one or more options eg recording quality before allowing you to continue.