The WORST thing you could possibly do if you want to copy VHS tapes is to buy a VHS/DVD recorder combo unit. So you at least haven't done that. Unfortunately, your post is short on details, making it quite difficult for you to get help.
What kind of capture device are you using to try to record video? Does it come with capture software? Generally those devices work best with the software that comes with them. If you don't have a capture device then explain exactly how you are trying to do this capture. Explain all the connections you set up to do it.
What kind of tapes are these? Commercial? Shows someone recorded themselves from TV years ago? Commercial tapes are often protected by Macrovision in the USA. If that's what you have then you may need to use a TBC to fix the signal from the VCR so it's recordable. This is part of the reason we don't recommend VHS/DVD combo units - you can't put a TBC between the VCR and the DVD recorder because they aren't separate units. You should probably also explain what you plan to do with the videos once you have them (ie. make DVDs, convert them to another format and keep that, etc.).