Did you check the checksum SHA1 of Manjaro KDE ISO if it is correct after download?
If yes,
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Please read this:
[HowTo] Provide System Information
and press the three dots … below your post and press theto give us more information so we can see what’s really going on.
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An
inxi --admin --verbosity=7 --filter --no-host --width
would be the minimum required information for us to be able to help you. (Personally Identifiable Information like serial numbers and MAC addresses will be filtered out by the above command)
Also, please copy-paste that output in-between 3 backticks ``` at the beginning and end of the code/text.