You need to give us more info. It could just be that that computer is slow. It could be that that computer does not have enough memory to run Ubuntu (unlikely but possible).
Also, it is not "Ubuntu" that is specifically designed to run on old hardware; it is Linux, in general. However, as days go by, more and more Linux distributions are dropping 32-bit support permanently, due to some very troubling facts (some of which people who love 32-bit should listen to):
* When companies and people maintain 32-and 64-bit builds of software, the 64-bit builds get more widespread use than the 32-bit builds, causing security vulnerabilities, bugs, etc., to go unnoticed.
* For corporations, the cost of maintaining 32-bit builds of 64-bit software, combined with the QA testing in-house costs, is substantial, especially when maintaining 300 plus packages.
Those are just some of the reasons why Ubuntu is working on eliminating 32-bit packages from their repositories. The only reason they haven't is because Valve threw a fit because they were going to lose their precious 32-bit compatibility. Really, that's totally a shame, this is totally the early 2000s. It really is. I totally have sympathy for them. (Not! There are packages out there, maintained by people, who give you all of the 32-bit stuff; why should Canonical maintain all that when others are willing to?)
Anyway, the dropping of 32-bit support won't come for some time. If the latest ISOs don't work for you, your best bet would be to go for older releases, fi they're even still available. If that doesn't work, you may need to go for a different distribution.
"On two occasions I have been asked [by members of Parliament!]: 'Pray, Mr. Babbage, if you put into the machine wrong figures, will the right answers come out ?' I am not able rightly to apprehend the kind of confusion of ideas that could provoke such a question." — Charles Babbage.
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