An overclocking flaw related to Intel's quad-core chips has forced Dell to stop taking orders for one model of its high-end desktop PCs in the US.

The $5,939 (£3,000) Dell XPS 720 H2C is a gaming PC which combined two Nvidia graphics cards with Intel's Core 2 Extreme chip. It's overclocked by Dell to run at a higher frequency than Intel intends and uses a liquid radiator to dissipate the extreme heat generated by the setup, a more expensive design than standard air-cooled PCs.

However, Dell told customers it would no longer accept orders for the 'bin +3' version of the PC, which runs Intel's QX6800 Extreme Edition processor at 3.73GHz instead of the 2.93GHz it was designed for.

"We apologise for having to do this, [but the] truth is that we do not have a line of sight to enough supply of QX6800 processors that can tolerate the Bin+3 overclocking," Dell's digital media manager, Lionel Menchaca, said on a Dell blog.

"At this point, our engineering team is doing everything they can to get more Bin+3s out of our original supply but this is expected to be a slow process," he said.

Dell asked its customers to cancel their orders and choose an XPS 720 PC with a slightly slower QX6800 chip or with a slightly less powerful QX6700 chip running at the same speed.

Intel stressed that there was no shortage of the chips themselves.

"They're taking these units that run at 2.93GHz and overclocking them, although we guarantee them at 2.93 only," said Intel spokesman George Alfs. "We're certainly proud of the headroom of the Core architecture and we're aware of them doing this, but once they start overclocking, it's their responsibility to support and warrantee the chips."

Dell thought initially it would have enough 2.93GHz chips that would tolerate overclocking.

"It just comes down to physics - a design can only tolerate so much voltage," Menchaca said. "When we started taking orders for the 720 H2C we had a fixed supply of the QX6800 chips that seemed ample at the time, but once when we found out how rare the Bin+3 variety was, we started combing our supply chain for even more.

"Last week, our backlog forecast started to pass our best estimates for finding Bin+3 chips. It just did not make sense to take any additional orders when we couldn't tell when we would be able to fulfil them."

This is the second time in the past year that Dell has delayed shipments of PCs in its gaming and enthusiast family. In August 2006, the company stopped shipping the similar XPS 700 model while it fixed a design mistake in the cooling assembly.