Computer restarts randomly

Hello guys.
Have a problem - subj.
First I found that cooler on CPU was installed incorrectly (hate these Intel box fastening). New thermal past and proper placement made CPU temperature OK. But restarts were still there. They became rare, but nevertheless. Was trying memtest, replaced power supply - nothing changed.
Could you please help me understand what was the problem?
My PC's dxdiag is in attachment, minidumps also.
Basicly configuration is following:
Core2Quad Q6600
Asus P5K
2 GB (2x1) Kingston DDR2 800
Radeon HD 4850 Gigabyte
FSP Epsilone 600W

Samples of savedump events:
- The computer has rebooted from a bugcheck.
The bugcheck was: 0x100000d1 (0x00000006, 0x00000002, 0x00000000, 0xb9e0c504).
- The computer has rebooted from a bugcheck.
The bugcheck was: 0x1000000a (0x000000e8, 0x00000002, 0x00000001, 0x806e4a16)

Thank you very much.

You have 0xD1 and 0xA (Twice) both errors relate to a bad device driver and all MiniDumps cite "Sacm2A.sys" which is a USB Cable Modem Driver.

Try updating your USB and Modem Device Drivers from your Manufacturers Website, if this doesn't work try connecting by a Ethernet Cable instead.

Thanx a lot =)
They are really old ... maybe updating will help