Ok, I'm one step closer now. I now know what causes my problem.
When I boot in -v mode I get an error with firewire drivers and then "Still waiting for root device".
But I don't have Firewire. Here are my specs a bit more detailed:

CPU Type AMD Turion X2 Mobile , 1600 MHz
Motherboard Name FUJITSU SIEMENS AMILO Pa1510 Series
Motherboard Chipset ATI Radeon Xpress 200M, AMD Hammer
System Memory 896 MB (Registered DDR SDRAM)
BIOS Type Phoenix (01/22/07)
Audio Adapter ATI SB450 - High Definition Audio Controller
Disk Drive WDC WD1200BEVS-07LAT0 (111 GB, IDE)
Optical Drive HL-DT-ST DVD-RW GWA-4082N
Network Adapter Atheros AR5005G Wireless Network Adapter (192.168.178.21)

Any solutions?