Windows 7: BSOD when idle for 1 hour.

My system has runned Windows XP Pro from the beginning. Since a few days, I have updated the system to 7 Ultimate 64bit (new install, not a upgrade).

After I updated the whole system and installed the correct drivers from Intel and AMD/ATI it ran fine. But after a few hours, I went out for an hour and when I came back, the system had restarted.
The first thing I did was changing the settings so it won't reboot on BSOD. I let it idle for a while and after about 50 minutes, a BSOD occured (IRQ NOT LESS OR EQUAL).



I had it scan the memory for 5 cycles with memtest 86 but no errors found.
Closer look at the dumps indicate that the first BSOD was MEMORY MANAGEMENT and the second IRQ NOT LESS OR EQUAL.

Any ideas?


- Windows 7 Ultimate x64 ?
- Age of system: 3-4 years
- OS Installation: 2 days

CPU: Intel E2180 socket 775
GFX: AMD/ATI HD3450 512 MB PCI-E
Mobo: Gigabyte EP43-DS3L rev 1.0
Memory: 1x MICRON 1024 MB DDR2
Memory: 2x Kingston 512 MB DDR2
Harddisk: 1x 500 GB Samsung SATA
PSU: ANTEC 420 WATT