If it says PC-100, then it is; unless it was made by "Typo Memory Company"... 
May be that it just bit the dust--usual reason for the constant beeps. I assume you changed the FSB slightly to overclock that chip--the older RAM probably couldn't take it. May have had something to do also with the different latency values on the sticks. But if the old one won't even let you Post, better to replace it.
Desktop: Intel i7 960 CPU @ 4.0GHz, EVGA Classified 4-Way SLI mobo, 12GB Corsair Dominator-GT 2000 DDR3 RAM, Crucial RealSSD C300 256GB Solid State Drive, Two WD 2TB SATA drives, 2x EVGA GTX 570 Superclocked graphics cards in SLI, Coolermaster HAF X full tower case, OCZ ZX 1250w PSU, Corsair H100 CPU Cooler
Laptop: MSI GT60-004US, 2x Seagate Momentus XT 750GB SSD Hybrid drives in RAID 0, 16GB DDR3 1600 RAM, GeForce 670M 3GB graphics card, Networks 'Killer' N-1103 WLAN card