Hi welcome to the forum. You need to convert the analogue output of the scart socket to digital.
Simplest way if you have a DVD recorder is create a DVD in DVD-Video format. Then copy the .vob file(s) to a PC.
If you have a DV camcorder with AV in you can use that to create DV digital files. These are easy to convert to 576i transport stream files which your box will play.
You could use a USB analogue to digital converter,these are sold to create DVDs from VCR tapes.
Lastly if your PC graphics card has video and audio inputs you could use these with suitable software.