Sticky PC Performance After Registry Backup.

My operating system is WinXP Pro SP3 (build 2600) fully updated, 1 GB upper memory, 2.4 Intel Celeron Processor, Motherboard ECS P4M800PRO-M478 1.0, two CD/DVD drives (LITE-ON DVDRW LDW-411S and SONY DVD RW DRU-190A ), and an external Maxtor hard drive backup.

For the last 2 months, when I backup the registry or the hard drive and reboot, the PC performs poorly - i,e,
A light on the front of the PC begins an unending cyclic blinking. Playing a video on the internet results in interrupts in the video and sound synchronized with the blinking. The Solitaire card game has interrupts when cards are dealt. Typing is sticky in MsWord 2007 The blinking and sticky PC performance can be ended by reinstalling the backed up registry and rebooting.