DDR2700 Memory Problem

Hi all, this is my first post!

I'm having problems with my memory! Can someone offer some advice, please?

Setup:
Asus A7N8X, Athlon XP 2600+, 2 x 512Meg PQI Generic PC2700

Scenario 1,
FSB 2x166, Memory 2x166, Both sticks of memory at 2.6V.
Windows XP will not boot!

Scenario 2,
FSB 2x166, Memory 2x166, Both sticks of Memory at 2.7V
Windows XP will boot but 3DMark2001 crashes!

Scenario 3,
FSB 2x166, Memory 2x166, One stick of memory ONLY at 2.6V
Windows XP will boot but 3DMark2001 crashes!

Scenario 4,
FSB 2x166, Memory 2x133, Both sticks of Memory at 2.6V
All works fine!


Could this be a problem with my old 240W Power Supply?

Thanks in advance.

gazbiggs