1gb 667mhz pc2-5300u ram not detecting on my desktop

hello friends.

i have a hp pavillion a1516in desktop.i purchased it in 2006 so it has low specifications.but it is original windoes desktop.
my problem is that i puchased a ram of specifications 1 gb 667mhz pc2-5300u-555 and i put it in the extra slot in my machine.but it is not detecting the ram.now i had a 512 ram installed on the other slot when i bought the machine.the max memory is 2gb so i dont know why it is not detecting my new ram.i interchanged the slots too to check if one slot is damaged but my 512 ram worked fine on the other slot too.so it is clear my new ram is not being detected.

now when i checked the hp site for memory specifications here is what i got:

Memory Installed 512 MB
Maximum allowed 2 GB (2 x 1 GB)
Speed supported PC2-4200 MB/sec
Type 240 pin, DDR2 SDRAM


also is it because my motherboard supports only till pc2-4200mb/sec so my new ram 1gb 667mhz pc2-5300u-555 is not detecting??