my 2007 imac only boots in t

I tried resetting my imac to factory settings. I deleted the hard drive and then I did some other stuff to it by dividing it ( don't ask why) when I deleted hard drive it was saying temporarily unavailable. Then I tried doing other stuff buy splitting the hard drive in half? Then I tried to eject the disk but nothing came out then I turned it off back on and now there's a flashing folder. Does this mean my hard drive is screwed.

I can only boots holding t and this weird icon floats around the screen.

I tried starting and holding command. Control r. And then with alt. Nothing. I tried with just alt just turns it back off. Only thing that works is t.

If I replace the hard drive and buy I disk should this work.

I had I think 1 tb Radeon 720 in it I think before. Or something like that.

I'm good at taking stuff apart and putting things back. But not programing. I just can't stop messing with stuff.

It's a mid 2007 model I really like this computer and bought it a year ago for 190.00 so I want it to work.

My kids were playing games on it and it just seemed like it just slowed way down. Which is why I tried to reset it. I just didn't save anything like I should have because I was not afraid of loosing personal info as it's just a quick web search computer. And you tube watch.

Any ideas will help.