1. If you're interested, try installing the 'important' or critical Windows updates (ignore the optional updates though unless you are sure they will be okay) to see if it helps with the genuine Windows issue.
2. There could be different reasons why your system is slower now, but if it works for you, you may want to just erase everything and reinstall Windows if you don't have a lot of data you are worried about to see if this makes any difference (you probably want to reinstall all the critical/important Windows updates though). Otherwise, there is third-party software that will supposedly clean out your system and maybe speed things up a little, but not something that I'm very familiar with honestly.
3. If you are having a problem with the fan, you can always try to buy one and replace it yourself or find someone to do this for you if you didn't already know.
You may be able to find other people to check your system, but if you wish, you can contact ASUS support if you want to send the system back for out-of-warranty repair although you may want to check your system first to solve any of the easier issues and get a better idea of the problems.
http://support.asus.com/Hotlines.aspx?SLanguage=enNot sure if you were more interested in finding out what kind of upgrades you can do rather than repair the unit, but hope this answers some of your questions.
Good luck!
