主语从句中存在三个语法错误：（1）引导词重叠（that whether）；（2）缺少主语；（3）冠词问题（ability前应该有定冠词the）.
建议改为以下的一种：
1 The difference between the winners and the losers is that the former has the ability to solve problems, while the latter doesn't have it.
2 Whether a person has the ability to solve problems determines whether he is a winner or a loser.
3 The difference between the winner and the loser lies in the ability or inability to solve problems.
4 The ability to solve problems differentiates the winners from the losers.