MacBook Air won't sleep

I bought this for my daughter about a year and couple months ago. this problem came up in a month after I bought, MacBook wouldn't shut down even I closed the lid. the fan was still working and making big noise. so I contacted to apple technical service. I asked them if this one had a hardware issue, I wanted to return and exchange, but one of your staff told me there was no hardware issue so I didn't need to return it. I followed the instruction what the staff told me to and the problem seemed to be solved like shutting down at that time, but I found out that problem never be solved. MacBook is getting too hot just browsing web and never be sleep mode when the lid is closed. these problems were never be solved from the beginning. please let me know how I solve this problem. thank you