Do you have keyboard software installed? The 'Defaults' of the keyboard can be modified w/ that. There's 1 for K/Bs & 1 for mice.
Anyway, if, indeed, it's doing abnormal, unrequested stuff whimsicly... Did this just start recently? Could a Sys Restore be tried?
If, it's a pre-loaded brand name PC, there are 'F' keys to initiate Recovery. This draws from a partition on the HDD. When done there are 2 approaches... we'll call Ful & Partial... 2 routes or options. Partial leaves added personals data intact & untouched. Full wipes the C:\ drive... both put the OS Back to Factory. BTW, Full & Partial, I just use here to get to point across,forget actual wording. W/ Full, wanted data must be extracted 1st to be replaced after the recovery is competed. Any programs, such as Microsoft Office or Adobe Photo Shop, games or whatever, would need to be reloaded.
I say this because, from this vantage point, I feel the repair is in the above. Although, run Malwarebytes, 1st. It feels like more than keyboard settings. What really throws me off, is the fact that you are not touching the Windows key... Shift + # , ah, no. I had to read you description a couple more times.
Is it wireless? Are the batteries good? Have you spilt anything on it? Is there dirt in it?
Drew