Mains power cut as fresh install flashing folder

[negativepitch]

Sorry if this is in the wrong section.
My old mid 2009 MacBook Pro has been a trooper but I decided to give it a compete spring clean with a fresh instal of my Yosemite.
Erased the hard drive etc etc. Went to instal a fresh copy got so far and I had not realised that my wife had unplugged it to do the ironing. And the battery went flat.
When I try to boot up now I just get the flashing folder with the question mark.
I have tried starting via the option key and I just get a blank light blue screen which if I hold down for what seems like an age I get the flashing folder.
I have tried it holding cmd-r but I get the same.
I have just tried it with my install disk and it tries to load but just gets the folder again.
The HD was fine so I don't think it is fried.
The software seems to have messed up.
I do not have an external drive and I also don't have another MAC apart from this iPad which is my daughters and I hate with a passion bloody things.
Any help/advice would be great.

 

[Riwam]

Sorry if this is in the wrong section.
My old mid 2009 MacBook Pro has been a trooper but I decided to give it a compete spring clean with a fresh instal of my Yosemite.
Erased the hard drive etc etc. Went to instal a fresh copy got so far and I had not realised that my wife had unplugged it to do the ironing. And the battery went flat.
When I try to boot up now I just get the flashing folder with the question mark.
I have tried starting via the option key and I just get a blank light blue screen which if I hold down for what seems like an age I get the flashing folder.
I have tried it holding cmd-r but I get the same.
I have just tried it with my install disk and it tries to load but just gets the folder again.
The HD was fine so I don't think it is fried.
The software seems to have messed up.
I do not have an external drive and I also don't have another MAC apart from this iPad which is my daughters and I hate with a passion bloody things.
Any help/advice would be great.

What is what you call "install disk" since Yosemite was not delivered with an install disk?
An external USB drive is nowadays quite cheap and always useful even when things work fine. Get one.
You must no doubt have as well a USB pen drive. If so, can you install Yosemite on it in order to boot from it, erase your computer disk and do again the installation?
Sorry if this is no help but in a difficult situation one must have additional means, an external USB drive, a USB key, a friend with a mac...
A non working mac all alone seems a problem with no solution.
Sorry to say that.
Ed