Random PC Lock Ups! Frustrating!!!

Yes folks, my 5 year old Compaq Presario 5000 is doing it's best to irritate the hell out of me again. >:(
It freezes at random and unexpected times: before/during and after Windows loads. When opening my first program (Firefox for example), even while typing up this message. Sometimes after it freezes, the monitor won't even come on when I switch it off and on again. It won't go through the BOOT sequence (currently set at CD -> floppy -> HD) It stops after the CD drive.
Over the past 3 years I've upgraded many parts on this PC. These are the current specs: (* indicates upgraded parts)
06e4h Compaq Motherboard
AMD Duron 700MHz
128MB Nvidia FX5200* (On AGP 4x)
640MB PC133 memory* (all unmatched, not necessary for this board)
100GB HDDs(80+20)*
250W PSU
52x CD Burner*
Now I know the list of possible causes of these random lock ups is near infinite, but I'm so frustrated that I'm hoping that through some miracle, someone here will be able to guide me through pinpointing that irritating anomaly.
I've tried everything, from a MemTest86+ scan, defragging my drives, to completely disconnecting every component and reconnecting them numerous times. The freezing seems to be independent of all this and still continues.
I know for a fact that my HD is slowly going bad and may be a cause of these problems, but I'm leaning to the posiibility of a failing mobo as well. Sometimes I need to disconnect my 20GB HD or the system won't find the OS on the 80GB HD. (Yes things are that bad
). I also get msgs saying that PCI.sys file is corrupt. Though those are rare. Other problems also include the system completely failing to recognize memory sticks. I only recently got it to see all 640 after removing and replacing them an infinite amount of times.
PLEASE! ANY help is GREATLY appreciated!
It freezes at random and unexpected times: before/during and after Windows loads. When opening my first program (Firefox for example), even while typing up this message. Sometimes after it freezes, the monitor won't even come on when I switch it off and on again. It won't go through the BOOT sequence (currently set at CD -> floppy -> HD) It stops after the CD drive.
Over the past 3 years I've upgraded many parts on this PC. These are the current specs: (* indicates upgraded parts)
06e4h Compaq Motherboard
AMD Duron 700MHz
128MB Nvidia FX5200* (On AGP 4x)
640MB PC133 memory* (all unmatched, not necessary for this board)
100GB HDDs(80+20)*
250W PSU
52x CD Burner*
Now I know the list of possible causes of these random lock ups is near infinite, but I'm so frustrated that I'm hoping that through some miracle, someone here will be able to guide me through pinpointing that irritating anomaly.
I've tried everything, from a MemTest86+ scan, defragging my drives, to completely disconnecting every component and reconnecting them numerous times. The freezing seems to be independent of all this and still continues.
I know for a fact that my HD is slowly going bad and may be a cause of these problems, but I'm leaning to the posiibility of a failing mobo as well. Sometimes I need to disconnect my 20GB HD or the system won't find the OS on the 80GB HD. (Yes things are that bad

PLEASE! ANY help is GREATLY appreciated!
