If Windows will not start normally, there are several things you can do to help diagnose the problem. You first need to take notice of any beeps or error messages the computer is giving you. Sometimes it will show a blank screen or just a flashing cursor, but even those are clues and can help eliminate other things as possibilities. Diagnosing start-up problems is only the first step; fixing the problem can be as easy as a few mouse clicks or as complicated as replacing a CPU or motherboard.
If Windows Will Not Start Try Safe Mode
Drivers, viruses or other software issues can cause your system not to boot. But you might be able to boot into Safe Mode. To do this, restart the computer and tap F8. You will see a number of options. Choose Safe Mode with Networking. If you are able to boot into this mode, the problem is likely software-related. If you recently installed or removed a program, you should be able to uninstall it or find a way to recover the missing files. You can also look in the Device Manager located in the System Settings of the Control Panel. You will often see a device listed here that has an error message next to it and can click through the error for a resolution.
Stop Programs From Launching
If Windows will not start normally, try disabling start-up programs. While in Safe Mode, you can try using the Microsoft Configuration Utility to prevent programs from loading when you start. it could be one of these applications that is crashing your system. To use the tool, go to Start>Run and type msconfig and hit OK. Look for the Start-up tab and uncheck any programs you recognize as unnecessary. Click apply and restart the computer. If the system still will not boot, you can remove any programs you recently installed via the Add Remove option in the Control Panel.
Run CHKDSK to Scan Your Hard Drive For Errors
If Windows will not start, you might have hard drive errors. You can use the chkdsk tool to scan your hard drive for file-system or physical errors. Assuming you can get into Safe Mode, go to My Computer, then right-click your C: drive and select Properties. Under the Tools tab, click Check Now in the error checking section. You will also see an option to Fix Errors Automatically. Make sure that is selected. Restart and the computer will run the scan.
If you cannot get into safe mode, you can open the case and look for the manufacturer of the drive (like Maxtor, Seagate, Western Digital, etc) and go to their website. Hard drive manufacturers will have diagnostic tools you can download and burn to disk. If there is a problem with the drive itself, you may need to buy a new one and reinstall Windows. This does not mean the content of the drive is gone forever. It might simply mean the boot sector area is damaged. Quite often, it is possible to put the drive in another computer as a second drive and pull that data off.
Scan the Memory for Errors
Windows Vista, Windows 7 and Windows 8 all have a built-in memory diagnostic utility. If you are running a previous version of Windows, you can download a program called Memtest86, burn it to disk and boot to it. This program will scan your RAM multiple times and look for read / write errors. If you are running Vista, go to the Control Panel, then System and Maintenance and then Administrative Tools. The memory Diagnostic Tool will ask you to reboot so it can scan. If you receive any errors, be sure to replace the RAM.
Solving your Windows start-up problems might be a long process. Make sure you try to eliminate any unnecessary devices that might be causing the problem. Unplug printers and other USB devices. If the computer is going into an old power strip consider plugging directly into the wall. Re-seat memory, check internal power, IDE or SATA connections to your hard drive. Make sure all fans are spinning and there are no red lights on the motherboard. Taking a close look at the internal connections, you might stumble upon the problem.