Windows Vista Boot and Explore.exe Problems

Hi Guys
running Vista with SP1, on reboot when trying to access Bios setup via "DEL" sometimes goes into Bios screen and then will not accept keyboard input, at other time just goes straight through to normal startup. I know I can reset the bios with the jumper but have just gone through fairly extensive overclocking and would rather not do it again. Computer is completely satable when it gets going.
Have just done major driver upgrades (Bios,MB, chipsets etc.) When computer boots normally have a major problem with windows explorer.exe as it stops working, come back eventually but very frustrating.
Would appreciate any help