Why has my hard drive gone from 80gb to 2047gb

It wont let me repartition because it dose not pick it up in windows. When i just plug my enclosure in it will pick that up as removable disk E: and it will load drivers for serial ata bridge etc,but soon as i plug hd drive into enclosure everything vanishes i look into pc management storage etc and there is no hd listed only my own C: so i cant do anything from there reformat or repartition.Other programmes pick it up like i said in original Q as being 2047gb i run tests on it read tests and write tests ect and reports no bad sectors.EASEUS partition wizard will give me option to partition but dose nothing when i apply just seems to stay on 0%.I know it is corrupted and unreadable just want to know of any programmes that would fix it.Ive tried WD website and tried there DOS CD download but like i said when i restar my pc with the hard drive attatched it freezes and will not boot up, the WD dos cd needs to boot from cd so it can detect your hds but with it plugged in it will not boot! Im doing this on my old spare pc running xp sp3 the hd drive is a WD 80GB note book hd. Thanks for quick response Anon, KINGER.