No problem, sounds like the same problem as me. Glad I could help you out because I know how crap it feels to not know why it isn't working!!

Go forth and mine!

I bought an Antec 620 HCG. Installed it just now and was able to load intensity 13 without the reset. I have tried to find this info all over the net without success, so hopefully this helps some people with the same problem:

Basically if you upgrade your card on an old system and the power supply can't handle it you will insta-reset, your computer will shut down or restart. The card must be drawing too much power and needs a better power supply.

Let me know if this helped you.

I am getting around 300 hashrate which is awful, so I purchased a proper 650w power supply today. I will install and let you guys know the results, in case there are any other internet fellows out there with a similar problem.

Hopefully my house hasn't burned down while I was out.

Aha, so is it impossible for the CPU, motherboard or RAM to be the bottleneck since all processing is done on the GPU? If so I will just replace the power supply.

Hoping to not have to grab a new motherboard, ram and cpu.

Power supply is widetech 655 platinum, it's probably about 3 years old? Thanks for the link I will check it out. System doesn't seem to be unstable, it's like a safety switch on my computer triggers and turns the whole thing off as soon as you engage an intensity higher than 11. Can't be temperature related I don't think because it happens so quickly. The shutdown is instant.

I am using a gigabyte 280x and a Q6600 on a oldish gigabyte motherboard with a 650w power supply. Currently I have it working at intensity 11. If I raise the intensity to 12 or 13 in cgminer my computer restarts instantly. Have tried putting the higher values in the config and also tried changing to them while mining was active, both fail and reset the computer instantly. I can't work out why this is happening other than maybe my mobo and cpu are too old or my power supply is too weak?

any ideas? As I said, it's working fine (but slowly) on intensity 11.

tried many configs, here is a typical one I use:
--scrypt -u XX -p YY -o stratum+tcp://URL --gpu-platform 0 -d 0 -w 256 -v 1 -I 11 -g 2 -l 1  --thread-concurrency 8192

Going crazy trying to solve this...