New Athlon PC failing - advice needed

[sclg]

MSI K8N Neo2 Platinum + Athlon 64 3500 Venice. 2 x 512 Mb Crucial DDR400 memory(*). Akasa Cooler. New 500W PSU and new SATA Hitachi disk. Using my existing CD/DVD drives & Matrox G550.
Put it all together and it started up OK. Default BIOS settings apart from setting the boot HD and disabling IDE. Installed XPPro + SP2. Hung once during the install but completed OK on rebooting.
Installed the drivers off the mobo CD.
It stops about 3 - 10 mins after any reboot. No blue screen - just freezes. CPU temp seems OK if I look when booting - c40.
Although I have built many PCs in the past, this is my first AMD one! I really have no idea what to try next. Any suggestions would be gratefully received!

Thanks

* Crucial memory (matched pair) was as recommended for that mobo on the Crucial site although it did say 2.6v on the site and the mobo seems to imply 2.5v. They are in DIMM 1 and 3 (the green ones).

[mike_w]

What PSU do you have? If it is a poor brand or generic, then that might be the problem. Also, you can check the memory by running Memtest.

[skuzgib]

Try putting more voltage throught the DIMMs

[kushtibari]

MSI manuals are a tad confusing. For dual channel put the ram in slots one and two i.e green and blue. I know it doesn't read like that, its just badly written.

[sclg]

MSI manuals are a tad confusing. For dual channel put the ram in slots one and two i.e green and blue. I know it doesn't read like that, its just badly written.

That's what seems to have fixed it.
Thank you all for your suggestions.
S