trademark question
 

I registered a domain which was free com domain and searched in google and found that someone do some emulators for games under that name,

so i checked trademark database and it was not there, now would you use that domain name?

In many jurisdictions it is not necessary to register a trademark, if someone else is carrying on business using the name, or uses it as a brand mark or similar and they can demonstrate that you registered it in bad faith then you could have issues.

Your English is fucked up...

The name of my company is the same as a few other companies both in the US and abroad. I use the .net TLD for my company. I have had various companies try to take it from me. None of them have succeeded since I don't compete with them in their industries. I also use the domain for reselling hosting which fits in with the .net TLD.

Depends on wether you intend to use it in the same industry as they do, and wether or not you intend to confuse people with it.
Wether or not it's a registered trademark doesn't matter though. they can still sue you if you use the domain in a way that can make people think it's related to their business in any way.

many / most domain names, especially those with decent generic keywords in them cannot be trademarked as they are "descriptive" rather than unique terms, i.e.: InternetSearchEngine.com = no Google.com = yes