100% Cpu usage - Hardware Interrupt calls!

Oh boy do i have something on my hands right now,  a computer a compaq Presario sr1615la that right from the start of windows xp login screen, is slugish and has a 100% cpu utilization,  we ruled out any kind of virus and rootkit, after searching and searching for  every possible hidden culprit, i opted to use  ProcessExp, a nifty great tool to find what program is hoggin the CPU, turns out the program identifies a "Hardware interrupt calls"  procces at 99%, Installing a fresh copy of windows on the same hardware yields the same result!

At this age and day, an interrupt problem reminds me of the past, where you had to reserve and give IRQ's for special hardware, sound cards usually where IRQ5, network cards where IRQ 9 or 11, and video cards where 9 or 14, and if you happened to have two diferent hardware cards with the same IRQ, things  usualy did not work at all , or made fort a very unstable system, these days we dont need to fumble with any of that, since the motherboard and operating systems work on the PNP method "plug and play"




Aparently the computer had been working fine for the past 2 years, upgrading the memory along the way and a vid card as well.,the customer claims that he noticed the slow down, since he connected an external usb hard drive four days ago.

Opting to resolve any IRQ mess the system had i disabled every single adapter and module on the motherboard i could, LAN, SOUND, SATA  ports (the hard disk is an IDE) Firewire, serial and Pararel ports but the problem persists,  Strangely when i removed the PciExpress Video card, the system did not present the problem.


Bad Vid card?  Maybe, but i noticed the power supply is rated for 235watts , and i doubt Compaq intended anyone to add a dedicated Video card with such a small PSU, the pciexpress slot draws 75 watts alone!, the vid card in question is a fanless Nvidia 8400GT, which while doesnt requiere an external 125 watts conector. it could well be the problem here

:UPDATE:
Sorry to have kept you waiting, We tested the system with a new 750 watts PSU and also a few Video Cards on the Same system , a Nvidia 9500GT, a 9600GT and a 9800GT, they all worked fine and the CPU utilization was at normal levels, The Video card that caused the issues, was put in several other computers, New ones and recent ones, and there was no noticeable problem and everything felt fine and dandy, Our customer claims the system was up and running correctly,  We also swapped hard drives installed Windows XP , windows seven and even UBUNTU and the problem persisted, slow and  100% CPU Utilization, my recommendation is that, a capacitor or resistance in either the Video card or the motherboard went bad and is causing the incompatibility, but given how well the 9800GT performed, he opted to swap onto it and enjoy the speed boost, after all his 8400 GS is a really old slow GPU and codl nto play any recent game.

I hope this helps anyone out the on the net with a similar issue. check for HARDWARE INTERRUPTS!

TACO FRIDAY :D!