Although it's possible, sweeping is not about instant gratification. It takes work, time, effort, consistency and faith on your part that you'll eventually win.
It's a hobby (avocation), not a job (vocation). You expect to be paid from your job (instant gratification), but you should not have the same expectation from sweeping.
The large or valuable prize sweeps attract the most entries from the most people, and the odds of wining decrease with each entry. The odds of winning can be right up there with the various State lotteries. You better believe that everyone here enters a sweep like the HGTV.Com - Rescue Your Renovation Sweepstakes where the weekly prize is $50,000. I wouldn't be at all surprised if the odds of winning that one is one in a million.
If your intention is just to win "something", then enter the less desireable sweeps that attract the fewest entrants.
I've been sweeping for more than 15 years - probably closer to 20 years. I don't remember winning anything the at all in the first year, and then some small wins started to come in . Others hit it big in the first few months.
As others have pointed out, the "instant wins" are the best bet to win immediately. Regardless of the games etc. that some instants make you play, the winning time(s) of the sweep are PREDETERMINED, and the game has no effect - Let me repeat that - the game has NO EFFECT (I always skip the game if I can, or I'll minimize it and go enter another sweep while the game finishes). If you're the first person to enter on or after one of the the predetermined times, you win. I once won $5,000 from Burger King on an instant win. I just happened to hit one of the predetermined winning times.
Make the effort, expend the time, do it consistently and the wins will eventually start to appear.