Computer won't turn on, yet power indicator is orange

I have a Gateway 700x or something like that, I bought it back in '03. A week ago I went on vacation and booted down my computer (or thought I did), anyway when I came back and went to turn on my computer the power light was orange (which usually means sleep mode) so I held the button down to power it down. It wouldn't shut off, no fans or anything or going though and if I hit buttons on the keyboard it doesn't boot up either. - It's like it's stuck. I tried unplugging my computer but whenever you plug it back in, the light comes on orange and stays that way. I tried the test button on the PSU but that didn't do anything.
After reading a couple posts here, I replaced the internal battery and also the PSU. Still no response and the light is still orange. I tried the test button on the PSU and it started up the fans and what not but still can't get it to boot up.
Since my computer is kinda old I'm not sure what's going on with it and if it's worth trying to take it to a repair shop or to just buy a new one and slap my hard drive in it.
HELP!!

 

When you went away on vacation did you actually unplug the PC?

And when you have tried to boot up the PC how long have you left it plugged in but not attempted to turn the PC on?

It is possible that leaving the PC plugged in for a day (say) before attempting to boot might be all that's needed.

 

sounds like a dead mother board to me.

 

No, I didn't unplug it when I went on vacation - I figured shutting down would be good enough. Normally my computer is on 24/7.

So what does that mean if my mobo is shot? Would it be more cost effective to replace it or buy a new computer? And if I bought a new computer, I should be able to install my hard drive in it...right?

 

If you can tell us your true computer model number, it may be able to be replaced quite easily. I don't mind doin a bit of research!

And yes you can transfer your old harddrive