MSI MS-6390 won't recognize CPU

Howdy....

I'm trying to piece together a system from differnt old computers I've gathered. The motehrboard I'm using is a MSI MS-6390VWA Micro-ATX out of a Seanix system. I've flashed the BIOS to the latest (1.8) without issue. After checking several sources (including the manual), it says this MoBo should be able to handle up to an AthlonXP 2000+ as-is. I'm trying to use an 1800+ (tested), but there are no options in the BIOS for setting the CPU speed other than the FSB clock (100-199). There is a jumper that switched from 100 to 133 FSB (currently set at 133), but the most I can get is 1000Mhz becuase it seems the MoBo multi is locked at 7.5 (greyed out). If I change the jumper to 100, I get a top speed of 750Mhz. If I increase the FSB number it won't post. I took a 1200 Duron out of it, so I know this MoBo can do more. Can anyone help?