MyMPx.org - Video File Format Error on DKY player

I've got another variation of the "video file format error" problem, which I'm not sure is addressed anywhere here in exactly this variation, so forgive me if the question has already been answered (and point me to that thread).

My son bought a $30 MP4 player from some online source, we aren't even sure where anymore. (I was not involved in the purchase and others cannot find the email about it.) We have of course also lost the manual, but it did come with an AVI converter program, and we do still have that CD for it, and have also installed the converter on our hard drive.

The identifying information I can find on it is as follows. It as a DKY brand, similar to this one, but without the camera, and only 4 GB. It does include the radio. The technical information says the capacity is 4 GB (3882.078MB, used 1971.546MB), and the version says TV5F568 V0.0.2.0 for software and TV1F568_V3.1 for hardware. I am unable to find anything about chipset, a brand name, etc.

A lot of the messages I read here refer to "rockchip" players, but I see nothing that would indicate this is one of those. Is it?

It plays .mp3 music fine. We have been unable to get it to play .mp4 or MOST .avi files. It gives "Video File Format Error". The .mp4 and .avi files are those downloaded from movieberry.com.

I *have* been able to get one AVI to play successfully. I used the AVI Converter that came on the CD (AVIConverter 3.0, 2006.09) to convert a short (20 second) .wmv file I had created a while ago for something else. The settings I used in AVI Converter were 320x240 resolution (the only option), Low quality (other options High or Normal), Aspect Ratio Full (other options 4:3 and 16:9). The only other options available were for the source file, target file, and scope. Nothing about frame rate or anything else technical.

Here's the big problem, though. When I converted this file successfully, the AVI Converter stopped at 98% complete, and stayed there until I closed the program. However, the output file was still available and worked, so that seemed okay. BUT, whenever I try to convert a larger file, specifically .MP4 downloaded from movieberry.com, the AVI Converter gets to 1% and just sits there forever, or at least until I get tired of waiting for it to move. I have left it go for at least 30 minutes, converting a 30 minute long video, and it never moves beyond 1%. Even if it's still doing anything, which seems doubtful, it would take so long to use as to be impractical. So I seem to be unable to use this converter to convert anything real.

Should I look for another AVI conversion program? There's no vendor name on this software. Do other references to various versions of AVIConverter refer to the same program, or are there lots of variations like there are players? Can I tell whether they are going to work for my device? I really don't want to waste hours and hours trying dozens of converters. Could it be incompatability with my PC? We are running Windows Vista (I know, I know... going to upgrade to Windows 7 soon.)

Thanks for any advice!