Agreed, in order of likelihood given the systems it is either drive failure (or bad cable connection to it), bad PSU, or memory.
I would stop running windows in case it gets worse to the point of corrupting important files or failing to quite booting.
Instead I'd boot to a flash drive/etc to run memtest86+ and again to run a HDD diagnostic. If you have another drive then I'd do a testbed install of Win7 on it. If you have another system then I'd clone your current HDD/SSD to it, BUT if there is already significant file corruption, there may be no smooth sailing until you reinstall the OS after the problem is pinpointed and fixed.
Of course you could just restore your partition backup, which we all make regularly, right?