Regarding the hard drive. You have boaught a new hard drive. Have you fitted this as master and reinstalled your software, or have you fitted it as slave for your files? Is the cd-rw/dvd drive recognised in BIOS.
Regarding the wires to the front panel. If they are led wires, you'll soon know if they are connected wrong because the wrong leds will light up. If you download and run AIDA32 click here, you should be able to find what motherboard you have and download the manual. This will tell you what connector is for what light. If any of the wires is for a switch, then you will either not be able to switch on, or reset the computer. If one is for the internal speaker, you won't get a POST beep.