I brought a faulty 20" iMac (A1174) that would not turn on for £40 but it came without a HDD or HDD Temp sensor. I have checked and it was the power supply that was faulty and I have wired it up to an ATX PSU to make sure I can get it working before I pay £80 for a mac psu. Running off the ATX psu I can now turn on the mac and get the chime and screen comes on, I can hold down the mac or option key and it lets me choose the boot device but no matter what I choose it just comes up with a circle with a line through. The fan below the HDD in the bottom corner is going full speed and I take it this is because the HDD temp sensor isn't there, would this be also causing the circle and not loading. If I just boot normally it comes up with a flashing globe but can't load/install OSX to change the startup disk. I have read you can short the wire for the temp sensor to fix the fan issue's. There are 4 holes in the HDD temp sensor cable so which ones do I short if this will help. I have also just tried to install OSX on to HDD that a put in a USB enclosure connected to my MBP but when I put that HDD in the iMac it still won't load but I have just realised that it was 10.7 and from what I've just read looks like this iMac won't run loin so might try that again with 10.6 Any suggestions would be great, Thanks.