If USD present some value, more USD means more value.
You're assuming the value does not change in accordance with the creation of more USD. It's certainly true that the change is not immediate, and under some market circumstances (like the current situation in the USA,) it doesn't change for quite some time because other factors are distorting the market as well. This is what is meant by economists when they describe money as being a non-neutral good. It isn't that prices all over the world instantly change to reflect the difference in supply of dollars, rather, those new dollars must be spent and circulated such that prices throughout the structure of production may be adjusted accordingly.
A decent PC always cost 1-2K during the latest 15 years
You're mistaking expected value ranges for an ever changing PC market for some sort of consensus saying that a "good" PC must cost 1-2K. But that doesn't make any sense at all, not only because there is no such consensus except that which supply/demand creates, but because a "good" PC is not one single good. It is, in fact, several thousand combinations of goods at any given moment, and those goods change over time. You can't possibly make the comparison here. It just doesn't make sense.
Before 1971, it was backed by gold, and after 1971, it was backed by nothing, but the purchasing power still holds relatively stable after 1971, of course there were inflation, but the value of fiat money did not drop to zero due to the consensus had not changed
The value actually changed quite radically in response to the halt in fixed rate exchange to gold...
http://research.stlouisfed.org/fred2/series/CPIAUCSLTake a look at the growth speed of CPI prior to and post 1971. That's a dramatic shift.
But beyond that, asking for dollars to become worthless (drop to zero,) to claim that anything other than your point was made is absurd.
Look... I think you honestly mean well, but you just don't understand the economics behind this. I would highly suggest that you find somewhere to take an intro to micro/macro economics course. This idea that markets choose things by consensus is well described by the idea of supply/demand, but you're blowing right past that relatively basic point then you're trying to discuss some things that require rather in depth monetary theory to find any meaningful conclusions.
I would also highly suggest that you read about the Subjective Marginal Theory of Value. You seem to be missing some key points in regards to valuations, and this reading will go a long ways to help you come to a better understanding about the whole of economic thought in general.
I would particularly suggest Economics in One Lesson by Henry Hazlitt. That is a fantastic starting point for all economic thought.
Good luck to you in these endeavors, johnyj.