I have a D505 and I had the same problem with 3.9 and 4.0 until I installed 4.0 to the hard drive then the screen resolution problem went away. Note that I like 4.0 a lot but its a little buggy.
Knoppix 3.7 works very fine on my notebook, but the 3.9 not.
Every time I boot it, the resolution is always 640 x 480 and I can't change it.
Any suggestion ?
I have a D505 and I had the same problem with 3.9 and 4.0 until I installed 4.0 to the hard drive then the screen resolution problem went away. Note that I like 4.0 a lot but its a little buggy.
I've been having trouble with v 3.9 on my d505 also. I get an x-server error during boot up.
I have tried some of the cheat codes and also seen some posts that suggest that the x-server error may be due to a flaw on the CD.
I'll keep digging for an answer.

Dell Poweredge R720 8SFF 2.5" x Xeon E5-2680 v2 2.8GHz 20-Cores 128gb 4x Trays
$349.99
Dell EMC PowerEdge R440 Xeon silver 4215 2.5GHz 16 GB ram 2x 550W PSU No HDD
$275.00
Microsoft Windows Server 2022 Standard 64-bit License & DVD 16 Core US Shipping
$34.99
Broadcom 9600-24i Tri-Mode RAID Controller 4.0 NVMe SAS SATA NEW 05-50111-01003
$639.69
Dell PowerEdge R620 2x Xeon E5-2630 v2 3.1GHz 2.5" 4-BAY 32GB RAM No OS 2x 495w
$168.95
Dell Poweredge R720 8SFF 2.5" 2x Xeon E5-2680 v2 2.8GHz 20-Cores 64gb 4x Trays
$259.99
Windows Server 2022 | Intel 18-Core Xeon | 32GB ECC DDR4 | 500GB NVMe | 3TB HDD
$898.34
Supermicro 1027GR-TSF 1U Rackmount Server 2x Xeon 2.3GHz 128GB DDR3
$219.99
Dell PowerEdge R420 Rack Server Intel Xeon 1.90GHz Six-Core 8GB DDR3 RAM
$95.00
WINDOWS SERVER 2025 [REMOTE DESKTOP SERVICES] 50 USER RDS CAL SEALED
$119.18