did you selected that video driver or did the system do it?
where do you see the information about s3?
i did a search on internet and found this information
http://www.ciao.co.uk/Productinformation/Fujitsu_Siemens_AMILO_L7300__6232122it indeed has a s3 video card, a problematic piece of hardware on linux, well, on windows too

if you have cli acces(console) you can reconfigure video, write su and then enter, it will ask a password and there you write the root password you gave when installing the system
then write XFdrake and enter, it is case sensitive, this will call a cli tool or a window(i hope the second) there you can select video card, monitor and resolution
press the graphics card/vendor/s3/unichrome base
if it doesn't work, you can try xorg/s3 or even vesa
"I might just do it more clearly, i can sit an hour or two, and suddenly disappear the screen and a split second after the logginscreen pop ups, and i lost All the works in have done Cry. Otherwise everything works great"
Sandalmanden , since your problem is completely different on completely different hardware you should create your own post to get the proper help, also post your system specs and don't forget to update machine and mention what apps are you running and the kernel you have installed