Abit AT7 Max2 Problems - Help!

I have assembled a PC consisting of an Abit AT7 Max 2 M/B, AMD Athlon
XP 2400+, 1GB RAM, Adaptec 29160 SCSI contoller, Creative SoundBlaster
Audigy2 Platinum and an ATI Radeon 9800 PRO. Recently, I decided to
upgrade the CPU, so I installed an AMD Athlon 2500+. This is where
problems started (or I didn't notice them earlier).

It is now possible that the PC won't boot up correctly (1 in 10).
Everything will come on, but there's no beep or video (screen remains
in Power save). Even more usual is that after a warm reboot (either
Ctrl+Alt+Del, or restart in Windows) the same will happen (7 in 10).
The only way to restart properly, is to keep the reset button pressed
for 2 - 3 secs, and the system MAY work (Usually a second 2-3 sec
pressing of the reset switch does the trick).

In addition, the system tends to hang. This is usually after the
screen goes into power-save (I have set the rest of the system not
to), almost after 30 minutes being idle. Then chances are that the
system will not wake up again (HDD light remains ON).

Now apart from the change in CPU, and the addition of a D-Link 520AB
WiFi card (which I subsequently removed to see if it made any change),
I haven't touched the system. I would swear that both those things
didn't happen before...

Have updated all drivers, BIOS etc etc etc.

Anyone having any ideas?

Thanks