Can anyone recommend me a cheap desktop computer? Or help me fix my error?

Checked properties and there is no read only lock. Only fired up the new computer for 20 minutes and then went back to my old one, if I keep it I will try the Classic Shell. Right now I going to try to sell it, first $250 plus shipping. HP computer

What’s the error message when you try to copy from the new computer?
What’s the size of the video file you are trying to copy?
How did you copy the video file to the new computer?

Here’s a WD support page:

I would take that External Hard drive out of it’s housing and plug it directly into the computer itself. I have has EHD’s that the housing circutry went bad (Western Digital EHD’s too) and taking the Hard drive out of the housing and plugging it directly into my machine worked. The hard drives inside are usually the WD Green Drives.

If the files are terribly important you may want to give this a shot, its actually quite easy to do.
They are SATA Drives (SATA are the cables that connect hard drives), so make sure your (older) computer has SATA instead of the IDE cables (large flat Ribbon cable) or you will need to insert it into the new computer you bought that does accept SATA.

Can you check whether your external drive is formatted as FAT32 or NTFS. FAT32 has file size limitations that could be exceeded if your video files are large. Most modern external drives should be NTFS.

(If you right-click the drive and choose "properties" you should find this info.)

Another possibility is that you may be tring to copy too many files into the root directory. What happens if you make a folder on your external drive and then try to copy the files into that?

Just some suggestions......