usually BIOS plays vital role in Standdby.
check ur manufacturer that if ther is mentioned that in SP2, if stand-by is failing, then u might need to upjgrade the BIOS.
check that out.
Intel Core2Quad 2.66Ghz 12MB L2-Cache
4096MB DDR Kingston Hyper-X
XFX 9600GT AlphaDog
Seagate 2 X 320GB SATA2
LG L246WH Flatron 24"