is my computer capable of upgraqdeing the hard drive because people here say that my computer is garbage and only good for office stuff. i want it for extreme gaming like crysis. they also said i need to upgrade my hard disk to 7200 rpm or my computer is trash.
A new hard drive won't allow you to run crysis or any game for that matter. A faster hard drive would only decrease load times.
For gaming you would need a video card. As far as I can tell, your computer only has an intergrated graphics chip which is only good for displaying the desktop. I doubt it has any gaming potential or even lossless blu-ray decoding for that matter.
With a 300W power supply, you should technically be able to run a ATI 5770 which can play crysis but I wouldn't call that extreme. Though im not too sure about that power supply and it's cappabilities to actually produce 300 continous watts. Best if you upgrade that to something that has an 80 plus certification and with 400W before considering better graphics card solutions.
An ATI 5770 would cost around $150 USD.
A good 400W power supply would run for $50.