If the PC has no spare interrupts, then some piece of hardware will not initialize properly. In the case of a SCSI controller which must have an IRQ to work, the SCSI BIOS won't load. If the IRQ conflict happens with the ethernet card, then the network will not start. These cases can be quite frustrating. The WIN95 or '98 resource manager will show no conflicts.
Nothing is wrong.
Instead of using one IRQ for everything, the Sound Blaster uses one, and so will the MPU401 chip. You can't afford to use more than one IRQ on a standard sound card these days. Spare IRQs are a thing of the past. Getting rid of an old sound card can improve your audio quality and use system resources more efficiently at the same time. A typical IDE PC is shown below.