Are you using the correct version of Kubuntu?
Have you changed any hardware since the last clean install (Contrary to what the Linux community says, not all later versions will run on older hardware and vice versa)
ISO is best run from disc if you are booting from it.
If you want to install from a USB drive at boot up follow the instructions on the Kubuntu website to create a USB version.

https://kubuntu.org/getkubuntu/

Hope this helps

Bill
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English Riviera:
Live entertainment, Real Ale, Great Scenery, Great Beaches, why would anyone want to live anywhere else (I�m definitely staying put).