The first problem, I believe, is the audio card;
at first, for "hardware" reasones: often audio cards have circuit for pre-amplify, tone control ecc. that can distort audio signal making packet reception bad, expecially at 9600 baud ("lost frames, high retries ecc.); to avoid that you can deactive all this circuit via software (when possible) or adding a jumper from audio card input to digital/analogic converter chip input (you can use the "line in" input so to have the "mic" input free for other applicationes);
so at first try using your audio card at 1200 baud under DOS (NO DOS PROMPT); if you have problem in this condition (you audio card must be well-configured under DOS) you'll have also under Windows, if you have no problem in that way than you can try under windows or at 9600 baud.
Remember that AGW Packet Engine need LINE IN input (ver.2000.50) so on some notebook it can't run.
I mean problems with IRQ, TSR software ecc.; I tested some "software-full" PC and all were OK; but sometime it's better to know what I'm going to tell you;
MICROSOFT PLUS: if you use Windows 95 and after 10000 tests you still have problems, try to kill it...
SCREEN SAVER: why use a screen saver? is it really necessary? it make more troubles than advantages.
ANTIVIRUS: often it's the cause of troubles, expecially when loaded at start-up and remains stay-resident. Try unloading it and resetting the PC.
TSR SOFTWARE: with CTRL+ALT+CANC key you can see all TSR and running software and (if necessary) unload it.
OTHER SOFTAWRE THAT USE THE AUDIO CARD: if you use flexnet, windows will not know any audio card (it's deactivated) and other software can not use it at the same time; but if you use agw packet engine, be careful: for example using winpack with agw, when a dx-spot spelling occurs, the reception stops.
Graphic accelerator can cause troubles, try with a low value (START > CONTROL PANEL > SYSTEM > PERFORMANCE > GRAPHIC).
Using hamcomm interface or baycom modem you could read that memory manager (HIMEM.SYS EMM386,ecc) can be the cause of troubles: in case of troubles see what's in your AUTOEXEC.BAT and CONFIG.SYS and try to deactive some lines..sometime it's work.
73 de iz7ath, Talino