What AreIRQ CHANNELS??

on saturday i tried to fit an extra hard drive & a new graphics card to my pc. i recieved the following errorRIVER_IRQL_NOT_LESS_OR_EQUAL(see other post). my main 250gb hdd isnt booting up. could it be this? i found this on a site(it says the error occurs when 2 pieces of hardware try to share the same irq channel): i found a site that says this: IRQ stands for Interrupt ReQuest and refers to special numbered channels that are used by devices to get the processors attention, for example, when you press a key on your keyboard this sends a signal to the processor via an IRQ channel (usually IRQ 1) to let it know that it needs to process some data.

IRQ conflicts can occur when new hardware is installed or reconfigured, for example, it can cause problems if you have your mouse on COM 1 (IRQ4) and a modem on COM 3 (IRQ4), below is a list of the default assignments for IRQ channels in Windows XP.
Default ISA IRQ Assignments
IRQ 0 System Timer
IRQ 1 Keyboard
IRQ 2 Cascaded with IRQ 9
IRQ 3 Default COM2 and COM4
IRQ 4 Default COM1 and COM3
IRQ 5 LPT2
IRQ 6 Floppy Drive Controller
IRQ 7 LPT1
IRQ 8 Real Time Clock
IRQ 9 SEE 2
IRQ 10 Open
IRQ 11 Open
IRQ 12 PS/2 mouse or Open
IRQ 13 Math Coprocessor
IRQ 14 Primary Hard Drive controller
IRQ 15 Secondary Hard Drive controller do you think thats whats happened?? what are these irq channels? how do i know what irq channel is what? is it to do with what power connectors i used to plug in the card & drive?