The hard drive is broken or missing. Check the BIOS to find out which.

If you haven't used it for 3 months, I'd suggest that the internal battery might have gone flat.

This is used to power a small amount of memory which tells the BIOS what type of hard drive you have fitted. It also powers the real time clock.

If the battery goes flat, these settings are lost and you might have to go into the BIOS to set that up again. But it's usually a very quick process.

Start by getting a new battery.
It's probably a CR2032, which is available from m ost hardware stores, supermarkets. They usually just slot in, via a readily accessible panel somewhere.
But in a few laptops you need a version with wires soldered to it, which gets more complicated.

Then you'll need to boot the computer, and see if it tells you which key to press to access the BIOS. "Del" is most common, but others I've seen include Ctrl-Shift-S, F1, F2, Insert, etc.

Once you've got into the BIOS screen, there should be an option to "Load Optimised Defaults" - select this, save&exit, then reboot and you should be up and running again.

From what you say, it would appear that the hardware of your laptop is OK, as it successfully passes the POST (Power On Self Test).

Thus the problem resides with the software. Try using the original Operating System Installation disc, to overwrite the Boot File and recreate the link to the operating system files, stored on the hard-drive.