Install and run a full scan with Malwarebytes,
in Safe Mode if necessary.
Next check condition of System FIles using SFC -SCANNOW Command
if necessary running SFC -SCANNOW Run in Command Prompt at Boot
If this doesn't help work through all the Troubleshooting Steps for Windows 7
starting with Clean Boot and Hardware tests.
Make your Repair CD now in case you lose boot: System Repair Disc - Create.
If so Troubleshoot Windows 7 Failure to Boot