Try resetting the unit to factory defaults and allow it time to sync once more time.
I have been having the same problem (fan stay on and NAS freeze up) for the past six months, this seems to get worse with this official 1.30 FW. The symptoms I have observed so far is as the temperature increases and at the same time some large set of data are being written, the fan will will kick starts and system will freeze up in about 10 seconds time. And connection to NAS will be lost, access the the web GUI is not possible but NAS LED is still working normally. Tried power down the NAS by holding on to the power button, the 'Shutting down ...' message will appear like forever while the fan is still blasting away (tried left it in that state for 24hrs before and it is still blasting away, always ended up unplugging the power cable).
A few days ago, I tried reset to factory default and reconfigure the setup to my own settings. Then encountered another freeze last night, it is re-syncing now. D-Link should be looking into this. This seems to affect people using Raid 5. I have 4x1T WD HD configured under Raid 5. I had also encountered a fan-blasting-freeze when doing a scandisk through the webgui.
I also recalled that using one of the beta fw version (cannot remember which one as I tried out every one just hoping to solve this big issue), this freeze never did happen for that beta version, the fan will kick start when getting too hot while writing data to the NAS, the NAS became not responsive for a few seconds then became normal and continue with the writing.