Over Heating

Well my computer started acting up the other day, I had noticed a difference in it as the temperatures outside warmed up it had started acting up and over the weekend I was watching a movie on it and it came to an abrupt halt. well after a few minutes when it did allow me to reboot I went right into the bios settings to the hardware monitor and noticed it was about 48 C. I had put this computer together back in February and it never much went above 38C-39C so I began researching it and made sure it wasn't full of dust. After finding no dust inside it I rebooted it without the side cover and duplicated what I was doing before and had no problems. The case I have is a cheapo Antec and it doesnt have a lot of room for extra fans or many vents so I ordered a new Raidmax case.
This case has lots of room for extra fans and such and the reviews other have left sound pretty good so I am hoping that will solve my problems and I can once again close my computer up. My wife says this is only an excuse to get a new case.