You've got a hardware problem. Linux gets its time from the hardware clock at bootup, and most RedHat-derived distributions (not sure about Mandrake, since it split from the main Red Hat tree quite a while ago) save the current time to the hardware clock at shutdown.
If you are getting random times, you probably need a new laptop. If they are not entirely random, you probably just need a new CMOS battery. Try the battery first, it's cheaper.
If you always boot connected to a network, you can set up ntp (network time protocol) and sync your clock to a trusted timeserver. If nobody local runs a timeserver but you are connected to the internet, you can use the US Naval Surface Warfare Center's atomic clock for a server.