I don't mean to be rude but you paid less then $400 for a 15" laptop. This probably should have been the first warning that you were not getting a high quality product. The second warning would have been the name ACER attached to the box. The third warning would have been the fact you were getting a laptop sporting an AMD Beema APU.
Now for other suggestions -
download
http://www.hdtune.com/download.html that app and check your hard drive speeds - you may need to look up your hard drive to compare its results to insure your drive is performing up to standards
you can try western digital's data lifeguard as well
http://www.majorgeeks.com/files/details/western_digital_data_lifeguard_tools.html to test the health of the hard drive
I suspect your basic problem will end up being either a bad/dying poor quality hard drive, or temperatures - temps are easier to check. does your laptop feel hot to touch (abnormally so?). If so you might be overheating.
Wayfall :
Very known issue:
http://www.tomshardware.co.uk/forum/id-2813275/disk-usage-100.html
if this is the cause then you have an overarching hard drive issue at play. either bad sectors (chkdsk) or heavily fragmented, or corrupted windows install, or dying drive.