The system: DOS 6.21, 386DX/40, Tseng ET4000AX video, 20MB RAM, sound was a Labway YMF-701 card followed by a GUS classic.

Background: Game was running fine, until the HDD died in an unrelated incident. I dropped a new HDD in and did a fresh OS install. (The previous install was still pretty new, so there wasn't much involved in getting it back to the same state). Labway sound card still in at this point.

Behaviour: SC2 is now the only game that won't launch. It starts loading, but then hangs at a blank screen.

I've now swapped the Labway card out for a GUS Classic, because it just arrived and it needed testing. That testing has gone great but the SC2 situation has not changed. I've tried SC2's startup switches with each card (/s:SBLASTER, /s:GRAVIS). I've also tried the colour pallette switch /g:BIOS.

Boot configs below. I'm using Phils startup configs for the menu, and none of the menu options have had an effect. The only other thing I can think to REM out of these is the CDISK driver for my external CF reader, but no help there. "SMONITOR" if you're curious is the Trident utility I use to force my Tseng to colour mode, which it needs for my CRT. Without this mode switch, SC2 doesn't even launch to a blank screen - it just dumps straight back to command line. In any case, SC2 worked fine with all these things before the rebuild!

autoexec.bat

1@REM ===== Gravis initialization (4.00) =====
2@SET ULTRASND=240,7,7,7,7
3@SET ULTRADIR=C:\ULTRASND
4@SET BLASTER=A240 I5 D1 T1
5@C:\ULTRASND\ULTRINIT.EXE -ej
6@REM ===== Gravis initialization ends =====
7@ECHO OFF
8
9PROMPT $P$G
10SET PATH=C:\ULTRASND;C:\DOS
11SET TEMP=C:\DOS
12SMONITOR C
13
14GOTO %CONFIG%
15:EMC
16:XMC
17:CMC
18LH C:\DOS\MSCDEX.EXE /D:OPTICAL
19:EM
20:XM
21:CM
22LH C:\DRIVERS\CTMOUSE.EXE /R2
23:E
24:X
25:C

config.sys

1[COMMON]
2DOS=HIGH,UMB
3FILES=40
4BUFFERS=40
5LASTDRIVE=H
6DEVICE=C:\FLASHATA\CDISK.SYS
7
8[menu]
9menuitem=EMC, Expanded memory + Mouse + CD-ROM
10menuitem=XMC, Extended memory + Mouse + CD-ROM
11menuitem=CMC, Conventional Memory only + Mouse + CD-ROM
12menuitem=EM, Expanded memory + Mouse
13menuitem=XM, Extended memory + Mouse
14menuitem=CM, Conventional memory only + Mouse
15menuitem=E, Expanded memory
16menuitem=X, Extended memory
17menuitem=C, Conventional memory only
18
19menudefault=EMC,10
20
21[EMC]
22DEVICE=C:\DOS\HIMEM.SYS /TESTMEM:OFF
23DEVICE=C:\DOS\EMM386.EXE RAM
24DEVICEHIGH=C:\DRIVERS\VIDECDD.SYS /D:OPTICAL
25
26[XMC]
27DEVICE=C:\DOS\HIMEM.SYS /TESTMEM:OFF
28DEVICEHIGH=C:\DRIVERS\VIDECDD.SYS /D:OPTICAL
29
30[CMC]
31DEVICEHIGH=C:\DRIVERS\VIDECDD.SYS /D:OPTICAL
32
33[EM]
34DEVICE=C:\DOS\HIMEM.SYS /TESTMEM:OFF
35DEVICE=C:\DOS\EMM386.EXE RAM
36
37[XM]
38DEVICE=C:\DOS\HIMEM.SYS /TESTMEM:OFF
39
40[CM]
41
42[E]
43DEVICE=C:\DOS\HIMEM.SYS /TESTMEM:OFF
44DEVICE=C:\DOS\EMM386.EXE RAM
45
46[X]
47DEVICE=C:\DOS\HIMEM.SYS /TESTMEM:OFF
48
49[C]

I must be missing something stupid, but I need some fresh eyes. Any ideas?

For reference, games that run without issue (performance concerns aside): Doom, Prince of Persia, Wing Commander, Wolf3D, Jazz Jackrabbit, One Must Fall, Epic Pinball, Pinball Fantasies, also the Second Reality demo.