If you're gonna replace your internal hard disk, go with ssd drive. min 250GB is enough for Installation.
And repair your existing 500GB and use it as a external hard disk.
DDR could cause a lots of troubles.
Same i too felt. I was using 500 GB HDD in my old PC, after i bought new PC i got 1 TB HDD which i never needed. All i needed was performance, so replaced it with a 500 GB Samsung Pro 850 SSD last year. I am yet to fill half part of the SSD. These days hardly anyone stores movies and large files on PC since many things can be kept in cloud these days.
1 TB is too much for one user who does not use pirated things. (Like me)
I also want you to try this..
Install any linux based os on your pc / run it as a live system.
Install gparted and try to delete all partitions from your hard disk..
Then try to run dban from live.. It'll delete a file which causes this problem with your HDD and replace it with 0's and 1's.
It's like a deep format.
700GB filled with games? did you buy all of them?
I used to play games alot. but if i complete them, then I'll delete them. by doing that I can save more space.
Installing this much of games could probably leads to troubles.