Gramma checking

Instead of just correcting the grammar, your passages need to be rewritten. Purely changing the grammar does not improve a lot the flow of your writings. The following is my suggested wordings and I have tried my best to keep your choices of words as much as possible.
Some companies often complain that hiring people who do not have working experience is a risk. They believe that these people will quit the job after a short period of time giving reasons like working hours too long or the job is too boring. Why does this happen?
It is because those companies have hired wrong people which result in creating troubles to the operation of the companies.
Comments:

Do not use always unless you really mean it. Always means all the time or every time. Often is safer in most of the situations.
Be careful about your choice of words. Guy is never a wise choice unless you really want to speak in that tone.
When you are talking about without experience, I think you are talking about without working experience.
Do not work for a long time is a bit ambiguous. To be precise, it should be do not work for the company for a long period of time. But it is clumsy. I have changed it to quit the job after a short period of time.
Technically, Why this happens is grammatically wrong although a lot of people speak in this way. If you want to say in proper English, it should be Why does this happen.
It is always a good practice not to start a sentence with Because. It is because or It was because should be used.
Hire should be in past perfect tense instead of present tense. This is an action that the companies have done in the past.
The wrong person should be changed to wrong people.
Sorry for being fastidious but I just want to explain to you why I have made such amendments.
圖片參考：http://hk.yimg.com/i/icon/16/9.gif

1. Some companies always complain that there is a risk to hiring a new employee
without any work experience, because many people do not think that a new employee will work for a long time, they can leave any time by giving many reasons, such as
working hours are too long & the job is too boring.why does this happens?

Because those companies hire the wrong employee, and it results in the
troubles for the operation of the company

by the way, what do you mean by troubles for the operation???

2006-10-20 00:15:13 補充：
1. Some companies always complain that there is a risk of hiring a new employee without any work experience,