You can "dual boot" but this is generally a pain, unless one of the OS is for very specific purposes (for instance, keeping Windows for games, since when you play you aren't doing anything else). Now, given the available disk and RAM, it is much more practical to set your mind on a main OS, on which you do most things, and to use a "Virtual machine" to run OS-specific stuff, and that you boot occasionally as an application inside your main OS. The performance of these VMs is very close to what you would get by booting them directly on the hardware (in some cases it is even better).
I have a lenovo B50/80 laptop. It works well. It came with win10 which I ignored as I have a linux disk to install from. Due to my sister buying it for me after work it's only an I3 with 4gig ram but I find it works well enough for Gimp as long as I don't want to do anything past laptop resolution. I find that keeping the drive half empty is a good thing. I have a backup external drive.
To keep you operating until you get the laptop fan fixed, or a new computer, you could buy a laptop cooler stand. I've just had a look on Amazon and they are available from about £5.00.
You sit the laptop on the stand and it has one or more fans, powered from a USB port, which blows air into the base of the laptop. Even if you get the fan fixed, they are probably worthwhile as laptops seem to struggle to stay cool - I know mine does.
As to the cable you are missing for your back-up drive, again these sort of things are very cheaply available on line. If you need to identify the correct connectors, we may be able to help.
When you have your new computer, the laptop could be a good way to try Linux. I use Ubuntu Linux now for everything and would never consider using Windows again.
Any way we can help, just ask. I will have to consult the experts as to the best way for me to upgrade.
Thanks David. I was thinking maybe I shouldn't turn it on without a working fan. I turn it off/sleep as soon as it gets hot but am unable to mutitask at the moment. (Play music while doing other stuff)
Hopefully, if it gets to hot, the computer should throttle its clock speed and everything will slow down dramatically! However, I don't think it is good for the thousands of solder joints on the printed circuit board to be subject to continuous expansion and contraction due to extremes of heat - it will eventually cause dry joints and intermittent faults.
A cheap laptop cooler (with or without the internal fan working) should provide the protection against damage. Just try to get one with large diameter, low speed fans, to avoid too much noise!
Hope this helps.
I am in the process of planning to build a new computer and trying to way-up all the alternatives (which change from week to week as new components are announced). I will probably ask the experts for advice very soon!