This may surprise you, but from time to time people do a regular clean out of files on there Hard drive , and uninstall programs or games they no longer use, or have finished using.
To make enough space to install new things.
Since windows does not automatically assume you don`t need the program does it.
User intervention one of the greatest flaws.
They empty there internet cache files because after a long time of internet use the cache file becomes very large as an example little people forget to do this.
Downloading cackware. for example by not paying attention or reading enough on exactly what they are clicking on.
Or just to darn lazy to keep some order of respect, for the junk they collect through there own usage of the laptop or system.
That is how you resolve the problem You change your user intervention with the device.
Keep a sense of order because the computer will not do it by its own, remember its you who tells it what to do, not the computer. So the question is who is at fault here ?
If a mistake is made on a computer is it the computers fault ?, or the human who told it what to do, or typed in something wrong?
An example is my computer was dead fast when I bought it, now its really slow what can I do? simple Uninstall all the bloody Junk you put on there yourself is a clear answer.
Do a check for a virus or any mall ware infecting the system.
No doubt picking up Viruses or mall ware by not paying attention to what you were doing in the first place when using the computer.
You see again user intervention, an in order to keep it running right, As you wish. Always bear it in mind to be tidy, and methodical with the way you use it,Keep track of things you are doing to it. It makes life simple. and there would be a lot of less questions about where has all my HD space gone ? It`s obvious You used it. Think about how you used it ? FYI you have one drive of 750Gb,
Its has no doubt been partitioned three times along the line pre system setup. since it`s a HP system. , so it will show as C: D: and E: it is one physical drive but the data size of the drive has been spanned across the three partitions made. So if you click on each drive see the initial size of each partition, add them up you will see the total will come close to 700Gb or so check that out.