|And just in-case you find the drive has started to die - even has died... It maybe possible to recover data from it nonetheless (see more below). Similarly it "may" be possible to resurrect the (dead) drive - albeit for a short while only - to allow direct access to contents... Details on request...|
Key item at this stage is not to try to write to the drive in anyway. Besides running diagnostics on it variously, also try booting system with an linux variant (Knoppix, Debian, Ubuntu) on a cd/dvd.
If system boots up OK with "Linux" disc then you may be able to access the drive and at least recover data etc to external storage media; after-which set about fixing the actual problems re' HD?
Be aware that running the recovery partition routines for most current systems will erase all data stored on the HD at the time; meaning you lose all your files etc.. So perhaps again first consider the option just above re' Linux boot up?
A remote/vague possibility... or two... This system doesn't have floppy drive and there is a non booting floppy in it? Is there a disc in the cd/dvd drive that you forgot to remove...; as the boot sequence is often (these days) cd/dvd first then (if no bootable cd/dvd found) the HD...?
Likewise the boot sequence hasn't altered since system was last working?
And is this a laptop or desktop?