Questions.
Can you try a system restore from the Advanced Boot Menu:
Advanced Boot Options
If this doesn't resolve, do you have a system disk for OS? if so try doing a startup repair which will fix issues with Explorer:
Startup Repair
long startup sounds like maybe a
driver issue or some other installed software. Were there any new programs installed recently? updates? new hardware? You can try running DriverVerifier to see if any driver issues are causing this:
Using Driver Verifier to identify issues with Drivers
If these don't fix the issue, then it might be a hardware issue. If you have a disk with Ubuntu, running it as a live CD is a good way to tell if your hardware is ok (generally)
I will be away for a bit, but I hope this helps point you in the right direction, also if you get a chance, fill in your system specs, It helps users help you