P5LD2 SE and CRC errors

I have CRC failure errors from WinZip, WinRAR and 7-zip for files that I'm sure that are ok, because I'm able to uncompress them in other systems from the same media (USB HDD).
Also, when I do downloads from the web, the files are, sometimes, corrupt.
The error occurs when I'm unzipping a file greater than 40Mb from an archive.
This happens in any kind of media ( HDD, USB HDD, DVD, CD, USB pen)
I've tested this situation in safe mode to get rid of network interferences and firewalls. The result was the same.
I've already upgraded the BIOS, drivers and utilities of all components for the most recent versions.
I've checked the cables of HDD, DVDROM. Also checked the RAM slots and tested.

The system configuration is:
Motherboard: Asus P5DL2 SE - BIOS 0605, 11/20/2006
CPU: Intel Pentium D 945, 3.4 GHz, 65 nm, rev D0
RAM: 1 Gb, OEM DDR2, 533MHz PC4200 (CPUz tells me PC2-4300)
Graphic: MSI ATI X1300Pro 256 Mb PCI-Express
HDD Hitachi SATA II 8 Mb cache 7200 rpm - 160Gb
Wireless Network: SMC 108Mbit PCI

I think that the OEM RAM it is not in the ASUS QVL table. Could this be the problem ?
I've noticed that DMI Information from PC Probe II tells me that the RAM speed is 37ns and the supported speeds are 70ns, 60ns and 50ns. Could this be the problem ?

What more tests can I do to identify the problem ? I have no spare components too test the system.
I think that should be something in the motherboard/RAM/controllers because it is common to HDD, DVD ROM and others devices.

Any help welcome.
Thanks