At least let us know if the windows came preinstalled or it is a custom install , and, if it is preinstalled, what is the brand ?
Do you have windows 7 installation disk or made a startup repair disk ?
The general cases, it is to check that if the hidden system reserved (or sometimes the recovery partition, based on branding) partition is active or not. And then it is to run startup repair, at least three times, with restarts in between every single run of startup repair.
But sometimes, it needs more care, depending on the situation.