Did you manually set your memory to factory specs? 
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When you start you should manually set the CAS timings and mem voltage.  Look on the side of your memory sticks (or box they came in).  There will be CAS and Voltage information.  It should be something like 9-9-9-27 1.65v;
Go into BIOS (hold DEL key till BIOS shows)
In BIOS under Frequency & Voltage/ memory configure: Set the "DRAM SPD: [Standard]"  in the next DRAM lines set the first 4 lines "by Typing" the 9, 9, 9, 27 for the CAS, leave all the others alone.  Now backup/ excape 1 level and set the DIMM voltage to 1.65v.  Scroll down to Vtt and set to 1.17v to 1.2v (within 0.5 of the 1.65v) as you have only 4GB total on 2 sticks.  Save the BIOS.
EDIT: If they still do not post, try 1 stick at a time.  If they still do not work, give us the type/ specs for the sticks and someone might have different ideas.   They may need to be RMAed. 

have you considered resetting the CMOS and trying again? The old settings for the previous memory maybe preventing  the system from loading.

IMO You should be able to change the values in BIOS with the old Memory in.  Then when you  do a save and exit, Immediately unplug the PC.  This should save the Old mem from damage and you can reinstall the new memory and see if Post will let you into BIOS and check all the settings.   see if you can do windows or whatever again succefully