Inspiron Desktop Memory Error: Machine won't start with any module in any slot

HI,

I'm having a problem with an older, Inspiron 580.  The machine had 4gb of ram (2x2gb, slots 1 & 2).  I purchased 2 additional identical modules and placed them in slots 3 & 4, but upon pressing power received the 2 beeps, and the machine would not turn on.  I then removed the two new modules and tried to turn it on again, but got the same result.  I've since tried every combination of module in the various slots, but the machine will not power on (either with the new or old memory, in any combination or any slot).

Any advice?  The machine was working fine before this, but now appears unusable.

Thanks,

S