The following presumes that you're following the instructions correctly, and that you've tried recording from TV to test that the machine isn't just having a hissy-fit with the VHS copies. Also, that you're not trying to copy commercial VHS which might include an anti-copy signal.
With DVD-Hard Disc recorders the first thing to go is always the DVD Recorder bit. I think a lot of the cause is that the hard disc is what's used most often, so no-one really notices the build-up of dust that affects the lens until it comes time to burn a disc.
First things first though, have you checked that the machine can play bought DVD films yet? If it can, then that's good news. It means that the laser is still okay. The next step is get the laser focusing lens cleaned up.
The best way is to whip the lid of the recorder off and clean with a cotton bud dampened with isopropyl alcohol. It contains virtually no water and dries quickly without leaving much of a residue. If you're old enough to remember cleaning cassette recorder heads then it's the same liquid if you used the proper stuff. Being brave enough to whip the lid off and having isopropyl alcohol to hand though usually indicates someone who would know how to do this already, and that might not be you, so let's look at the alternative as well.
It's a DVD Lens Cleaner disc. (Looks like a ordinary blank silver DVD but with a tiny brush poking up from the surface.) The idea is that as the disc spins, the brush wipes away dust off the lens. That's okay if it's dry dust. It's not so good if there's any sticky coating on the lens from airborne pollution. This can come from some plug-in air fresheners, smoking, cooking residues in open plan homes. For these reasons the cleaning disc can be a bit hit or miss.
Once you've had a go at cleaning, try playing back any disc that you might have previously recorded on that machine. If the laser can do that, then there's a fair chance it can burn a new disc too. You might want to try a DVD-ReWriteable (DVD-RW) disc in the machine just to get the hang of the ins and outs. Being re-writeable, any slip-ups can be erased and recorded over on an RW disc.
