First I need to say that I am unsure exactly which model my current laptop is but I'm fairly certain it is the inspiron 5521 (looks like this though, i15RM-5125sLV). I'm wanting to get a new computer as this one has been having trouble and is a bit banged up. Would I be able to swap my current hard drive with the hard drive of the inspiron 5000 series (Inspiron 15 5000 Non-Touch from dell website) or if that isn't possible trying to buy the same model and swapping those hard drives. I know that there may be problems with the drivers and possibly some software like Microsoft office, but how likely are those problems and will it even fit? Would backing up the current hardrive then recovering the backup on the 5000 series work? Sorry if this is long I'm just unsure about how it all works. Thanks.
You will face any number of issues, starting with the hardware -- if the existing system has a 9.5 mm hard drive, it won't fit most newer systems, which require a 7 mm or slimmer drive.
The odds of being able to successfully boot a drive with an OS installed on a foreign platform decrease as the differences in hardware increase.
Further, new systems with Kaby Lake and Skylake CPUs don't support (or don't support fully) Windows 7.
Essentially, you want to build a brand-new house on an old foundation - generally not a good idea. It may or may not work - you won't know until you try, but have a backup in case it doesn't work (and the odds of that are high).
I current'y have windows 10. If the new system also had windows 10 would that increase the chances of it working. I will still have the problem of the hard drive size, but that is an easy check. What you say makes sense. Thanks.