My computer won\'t download or install anything new, how do i fix it?

Basically to cut a long story short I tried downloading flash player again and it gets to 47% then says 'unreliable source' at first I thought it was just adobe, However I later found out that it was not adobe. In fact it is my computer that just will not download anything at all. Either the same message comes up or something similar such as corrupt source/data or even the progress bar will just freeze and nothing will happen. Also I have tried different browsers and the same thing happens. I have made sure my security settings are correct and everything seems to be in order. I have even removed some programs that could be contributing and blocking my downloads but after many days and much frustration I am still left with this problem and I can not seem to find anything on the internet. So if anyone could help I would be very appreciative and I am happy to give who ever more information if they require it.