There are a few possibilities here:
1) The column may be clogged, try running your Mini GC at high heat and pressure for an hour without injecting anything. Then inject a sample of acetone at the default temperature/pressure profile settings. If this does not fix the issue and you have followed other troubleshooting tips here Best Practice Techniques for Vernier gas chromatographs then email chemistry@vernier.com for further assistance.

2) The detector (MEMS chip) on your Mini GC may be damaged and may need to be replaced.
It is very difficult to determine when the MEMS chip (the detector) of a Mini GC needs to be replaced. The normal life of the MEMS chip depends on frequency of use and the types of compounds that have been injected, but in general these effects are not clearly understood. The most reliable symptom of a MEMS chip going bad is that the peaks will be less and less high, taking more volume injected to reach the same peak intensity. However, this is also dependent on the sample volume.

3) Make sure you are comparing peak heights within the same instrument. Peak heights will vary from unit to unit. This is especially true between different versions of the Mini GC. Peak heights will be different from the original Mini GC to the Mini GC Plus and to the Go Direct Mini GC. The Go Direct Mini GC has a different detector compared to the pervious versions and will give different chromatograms because of this. See Go Direct Mini GC Compound Library for examples.

If your Mini GC is producing very small peaks, compared to peaks from previous injections of the same volume of the same compound, and you have followed other troubleshooting tips here Best Practice Techniques for Vernier gas chromatographs then email chemistry@vernier.com for further assistance.