Without USA would us British people, definitely have been conquered ?
Or could we have defeated Hitler without them?
I think that the UK wouldn't have been conquered as such (at least not for years, if ever) but would probably have become sidelined as Germany strengthened its hold on conquered land and expanded elsewhere. I don't think the UK could have held up enough
economically to fight effectively for much longer. With the UK more or less out of the war through not being able to make enough stuff quickly enough, much of the resistance to Germany would have collapsed everywhere apart from the USSR. Everywhere else was either too far away and/or not strong enough to fight alone. Germany couldn't have conquered Britain outright at that time, but with this scenario they wouldn't have to. They could conquer Britain or make it a de facto vassal state later.
Buying help from the USA cost the UK a vast amount, though. The USA had a seller's market and knew it. Not only money (the USA had far more of that than the UK anyway), but land, technology and influence. That extended past the war, e.g. controlled transonic flight was invented in Britain, but it was shut down by the UK government and given to the USA.
Obviously, it was in the best interests of the USA to do what they did. Not just to gain power while reducing Britain's power, but because they would have ended up fighting sooner or later and it was much better for them to fight sooner with allies and in other countries than alone and at home. If they got a chance to fight at all - Germany was working on a nuclear bomb and would probably have succeeded at some point if they weren't so hard pressed in the war. Likewise for long range missiles. They might have been able to nuke the USA by maybe 1950 and does anyone think Hitler would have refused to give that order?
EDIT: The post about the people at Bletchley Park not getting due credit reminds me of some other people who didn't get due credit - the sailors of the USA and Canadian
merchant navies. Repeatedly crossing the Atlantic in civilian ships with the ever-present threat of German submarines was a very courageous thing to do.