gpu temp 42 on idle and 100 on load

specs:
intel dh61ww motherboard
intel core i3 2100 3.1ghz
6 gb ram
600w psu
1tb wd hdd
ati r9 270x dd 2gb

i recently bought the gpu and installed a new hdd too. When i tried to create partition on the hdd during windows installation, the system waits for sometime and the it shows no hdd found. So i reset my computer but didnt switch off the power connection and opened boot menu and there no hdd in the menu. This time i switched off the power connection and started again. Now there was the hdd in the boot menu. So i started the installation again but the same thing happened, when trying to create partition the system waits for some time and then it shows no hdd found. So then i changed the sata cable and port and started again. This time the partition was created and the os got installed. So then i installed the gpu drivers and everything else. Then i started a saints row 4 and it too 5 mins to load the game and ultimately it didnt load after the cutscene. So i tried minimizing the game but it didnt minimized and the system hanged. So i reset my pc and then installed dota. When i started a match in the game the game loaded easily and there was no lag whatsoever. After 20 sec of playing the screen freezes and becomes normal after 2-3 secs but without sound and again freezes and become normal again but this time with the sound. This happens again and again but different sound stops on different freezes(sometime the music stops and the fx sound runs, after next freeze the fx sound stops and music sound comes alive and after the next freeze both stops). So i switched off the game and saw the taskbar was short(wtf). Opened start and tried to click restart but the button hanged but the destops icons was working. So i tried opening the catalyst center but it showed me so file not found and some signature thing i dont remember. So i reset again and installed furmark and stared benchmark user setting(resolution 1280*720 and no aa). It showed me some frames and the temprature was 45 degrees, while the benchmark i open gpu shark with was available on furmark. There it showed 100 -102 degrees. I was shocked and started catalyst center(this time it opened) and tried to see the temperatures and it also showed 100 degrees. So i stopped the benchmark and the temp came to 42 degress instantly and after the same thing happened the taskbar hangs, start menu don open up etc. Same thing with gpu z. The only thing that bothers me is that in the furmark benchmark it shows 50(max) while running but gpu z, catalyst, gpu shark shows 100. So my question is that is it the fault of the hdd that is somehow has corrupted the gpu drivers and thus showing the wrong temp in gpu z , ccc, gpu shark because they all use the drivers to display the temps or it is the fault of the gpu itself.

What OS are you using? Also, have you disabled the IGP? What case and how many fans, any other cooling used?

100°C is a bit warm but the card can run, maybe not stably, at that temp. I suspect there are cooling and driver issues, hence my questions.

Biggest. Paragraph. Ever.

100C is NOT good for GPUs. They will all throttle, get unstable, shutdown, by that point. I doubt its drivers (I personally have not seen a driver cause a temp issue).

I also believe, but am not certain, that temps will be read regardless of drivers. If it is shutting down/having problems, its the right temp. Sensors are hardware and software reads the sensor AFAIK.

Are the fans working on the GPU?
What does your case airflow look like? What case?