Windows freezes at startup. Can't reinstall windows.

does the problem occur always at the same spot, or is it random?
1. take your pc apart and vacuum all the parts and get the dust bunnies out. clean the fan and make sure the processor's heat sink is clean. you can do this without taking off the heat sink from the cpu. if you take off the heat sink, you will need some new heat sink goo.
2. make sure you touch a metal part of the case to destatic yourself
3. put your pc back together with only one memory chip and only cd rom. do not connect anything else
4. in the boot sequence, try to get into the bios. press 'esc', or 'f1', or whatever key it tells you to press to get to bios
5. if you can get into bios, you computer is working, sort of.
6. go through each option in the bios. don't worry about messing it up. there's an option for 'default settings'. maybe you should pick that one. the bottom line is if you can use bios, your pc is working
7. your boot cd, windows or linux, should have an option for memory check. give it a few hours to check the memory. turn it off, swap out the memory stick, repeat. turn off, add both memory sticks, repeat. you should be sure your memory is working flawlessly.
8. turn off pc, connect hdd. there will always be an option to format the hdd. format it. sometimes a boot cd will have a hdd test program, just like the memory test.
9. if you get hung up at any of the previous steps, pay attention to whether you can repeat it. if it's randomly crashing, you might have a bad power supply. make sure you have a good power supply. swapping out the p.s. is always a hassle, because sometimes you can't take it out without removing the motherboard. a power supply tester is nice, but not always reliable.
10. if your pc was full of dust bunnies, it could be that it was overheating. if it's clean and randomly crashing, you might have a bad power supply. if your hard drive will not format or if you can't install the operating system, you might have a bad hard drive.
11. don't be afraid of your computer. take it as a learning experience. it isn't brain surgery or rocket science. don't rush it. you will need some time to go through the process.
12. additional research is always a good thing. never hurts.