HTPC locks up when idle

[Topher5000]

TV-Server Version:
MediaPortal Version: 0.2.3.0 RC1
MediaPortal Skin: Blue Two
Windows Version: Windows XP (SP2)
CPU Type: AMD X2 3800
HDD: WD 320gb + WD 500gb
Memory: 895mb
Motherboard: MS-7207PV (MSI) K8NGM2
Motherboard Chipset:
Motherboard Bios:
Video Card:
Video Card Driver:
Sound Card: Realtek High Definition Audio
Sound Card AC3: coaxial out
Sound Card Driver:
1. TV Card: Hauppauge
1. TV Card Type: PVR-150MCE
1. TV Card Driver: 2.0.43.24054
2. TV Card:
2. TV Card Type:
2. TV Card Driver:
3. TV Card:
3. TV Card Type:
3. TV Card Driver:
4. TV Card:
4. TV Card Type:
4. TV Card Driver:
MPEG2 Video Codec:
MPEG2 Audio Codec:
Satelite/CableTV Provider:
HTPC Case: nMedia 280
Cooling:
Power Supply:
Remote: MCE
TV: Hitachi PJ-TX100
TV - HTPC Connection: HDMI

I leave my HTPC on 24/7 since I the one HDD is a share for a modded Xbox in another room. To save power & heat, I have the HDDs set to power down after 15 minutes of idle.
While it's idle, MP is on the home screen. After a couple of days without use, the computer totally locks up. The front display stops scrolling, the time stops, & there's nothing I can do.
When I power down, the display still shows whatever MP screen it was on last. I have to flip the switch on the PS, wait a few seconds, flip it on & power the computer up.
Sometimes there won't be any display over the DVI output (DVI to HDMI switch via a DVI-to-HDMI cable & then HDMI cable to my FP) until I reboot.
Is this a memory leak, or a problem with the PS or cpu or what? I have the nMedia PS that came with the case, but it wouldn't start up when I had an AMD 3000+ as the cpu since there wasn't enough draw. I can try it, but I really don't think that's the problem.
EDIT: I should say that while it's locked up, I can still access the shares over the network with the Xbox.

[Paranoid Delusion]

I should say that while it's locked up, I can still access the shares over the network with the Xbox

I would say if the network was still accessible, xp was still running, so may it be a GUI\graphic output problem from the mother board itself.

Would also be concerned about the 3000+ processor (take it as not being faulty) not being able to power up, as that would mean the power output from the supply must be really borderline as to whether it works or not.

Not easy to identify exact problem, but does this also happen if PC left on without MP running (then useless as a htpc ha), if ok without MP running, set logs in MP setup to debug and then duplicate problem and post logs.

[Topher5000]

Sorry for the late reply, I was away for the weekend.
I'll see if it does it without MP running.
As for the 3000+, when I first assembled the htpc, I thought the PSU that came with the case was faulty, but after reading at spcr.com, I found out that a lot of the high-efficiency PSUs need so much load to start. Apparently since I only had the mobo, cpu, dvd, Hauppauge & 1 HD, there wasn't enough. If I had used a seperate video card, I would have been fine. I haven't tried it with the 3800+ yet.