Hard drive issue?

I have a 2007 iMac that just yesterday starting having problems. last night it started with the flashing ? folder. Following some advice on a thread, I disconnect and then reconnected the hard drive. That seemed to do the trick and it was working fine again this morning. This afternoon it crashed again and after rebooting it would show the apple logo and the black loading bar would get about a third of the way up before it would just switch off.

I booted up in recovery and looked in disk utilities, tried a repair but it said it couldn't repair the disk. I tried the same thing as yesterday but to no avail. I felt pretty sure it must be a hard drive problem. However, I have a windows bootcamp partition on the hard drive so I thought I'd try that out before I went any further. I booted up, held the option key and chose the windows partition and it's loaded without any problems.

So my question is really, if my windows partition is working, does that mean my hard drive is ok and there's just a problem with my main partition or could it still be a problem with the hard drive?

Thanks in advance for any help.