Wow, between my 4 A1200s I've never had a problem with any of them supplying enough power for a 2.5" hard drive and modest accelerator. Laptop hard drives nowadays use *tiny* amounts of power. My first guess would be the cable - it's very easy to misconnect the cable to the A1200 board as the pins are "bare". Miss the last row and your drive has no power. Get it backwards or miss it off the other end and you can fry your drive, cable and/or motherboard.
Edit: I'll add to that that 2 of the A1200s also supply a CD-ROM drive, and all work on the standard A1200 PSU, and HDs varying from 30GB to 120GB...
you attatch the red stripe to the ide conecter to pin one side or side further away from the back l dont think u can blow up the hd never happened to me
my 2 2 1/2 orginal commdore cables showing there age try reconecting to mb few times
and sometimes just if cable bent in wrong shape stops even orginal 40 meg drives spining up if dont hear hd spining after 30 secs turn the power of and try again. make sure the
pins on mb are not bent or broken where cable conects
also if your using 2 1/2 ide drive make sure the blanked of hole on the cable
goes to the hard drive pin 1.2 do the powering of the drive if you using cable
designed to fit 3 1/2 drive these are cut of the cable,
also if its a 3 1/2 drive forget about powering from standred 1200 power brick
you need at least 500 psu l powered a blizzard ppc and 3 1/2 of 500 brick
but also had feed from the floppy conector when was in a tower with bvsion card as well
cool you have squrriel scsi loved those really cool addon wish keep mine
