I have been running a RAID1 array for the system disk on my computer for the last three years. It has failed on two occasions, both of which were due to repairs being carried out (replacing the DVD R/W and, recently, the graphics card and power supply). In both cases the machine continued to re-boot and operate correctly, but showed the array as 'degraded'. This was cured by running the nVRAID manager utility which re-built the array - took a few hours but no data was lost.
I find it difficult to imagine how you managed to arrive at a striped (RAID0) array on a single disk - it's possible, but unlikely to happen without very careful planning. What RAID system are you using, by the way?
You need to use the RAID diagnostic utilities to check on the present status of the array; first, whether the HDs themselves are healthy (otherwise you need to replace the failed disk). If they are ok, and one of them still carries its copy of the original system, it should be possible to re-build the array using the utility provided for that purpose. If the other has been corrupted, it may be wiped clean before re-building the array.
You should be able to inspect the non-system disk (the one 'just there'). It should have an assigned drive letter, and carry the OS and data as it was before the array 'broke'. I assume you have every thing backed up just in case you have to start from scratch again - but, I repeat, this shouldn't be necessary.