Hi, I am new to this forum. I am not a Techie. I saw MAGIC ANDRE's Dec 2009 response to 'How to get the cause of high CPU usage by DPC / Interrupt'. I think he can help me to get rid off this maddening experience of my system slow down. It logs in with in 70secs and maintains a very decent speed in its operations. But during the course of an application or even when it is idle the CPU usage climbs to 100% and the sys starts crawling. becomes dead slow that makes you go mad. Media files cannot be played, if you try you get outlandish noise from the speakers and never recovers till you restart the sys. I am not able to identify the process which evokes such reponse from the system becz it may happen at any time. It may not happen at all on a given day. Now I have been working with it for the last 40mts with out this nusense but after restarting it for four times prior to that in an hour of work. I have tried everything, through scanning by antivirus, malware, etc system is clean. I have registry cleaner(uniblue) and system speedup(amigo) tools with no help. Process explorer indicates an idle process of 90%(when no application is running) when the system is alright but in the slow down state idle process is either 00 or upto 10%. However 'hardware interrupt' in PE jumps to even 50% once the system slows down. When the system is normal it would be < 1.5% the specifc of my system: Processor: Pen 4, 2.26gh Hard disk : 2 nos. 80Gb and 160 Gb with operating system in system-partition of one of these disks. there a 6 partitions. RAM: 1 GB DDR1 OS: Windows XP SP 3 I have formatted all the disks since i started getting this problem with out any result. I know vry little abt computers, but i have taken this as a challange. Every day I am spending a lot of time visiting a lot of web sites and trying every possible trick to set this right. When the machine behaves you love to work with it. Would appreciate help from any member of this forum.