Minecraft – Why does Minecraft say that ‘mob:ghast:fireball’ does not exist

The portal spawning algorithms have gone though a lot of changes to get to the point they are now, and it used to be the case that you'd end up miles from your base when this happened but Notch linked them properly so hopping back in your Nether portal should take you right back to where you came from. As with everything Minecraft, this is not a guarantee however!

As StrixVaria said, carrying a compass is vital to helping you get back from any expedition but this does point to your spawn, not your base.

Shinrai pretty much has it right for what likely happened.. Crashed game will not save the chunks so the portal never got generated and the Nether likely regenerated fresh, again, when you loaded the world back up again.

However.. easy way to solve this is go back to as close to where your portal led you the first time, and die.. You will go back to the over world. The nether will be saved -including- the items you just dropped from dying. YOu should be able to hop into your portal again and while it -WILL- generate the portal in a new location (9 out of 10 times atleast), it will be close to where it was the first time, and you can go pick up your items again..

Just do not die near fire or lava that may destroy your items when you drop them.

EDIT: To estimate where the portal will appear in the nether from the overworld coordinates, divide the over world coordinates by 8.. But remember that the portal is somewhat randomly placed from that location to be within 128(ish) units from it.