Blinking Cursor up Lft corner PC frozen

It may be a corrupt master boot record,insert the startup disk in your floppy drive and boot the system,at the command prompt,type in fdisk /mbr,reboot.
when the system comes back up,select to run setup without cd-rom support and load the files fomthe disk,after the process completes,remove the drive and see if this fixes problem.
If the bios detects a problem during boot process it will give a beep.

Before anything else, make sure you do a virus scan. From the wording of your question, I believe that your system boots up correctly, and you are able to work in Windows for a while...then something happens to make the screen go blank and leave you with a blinking cursor. If this is truly the case, there are a few things that could be causing your problem. The first thing to check is the CPU fan. It must be spinning fast enough to keep your processor cool. If it isn't working properly, orthere is something blocking the airflow, the blinking cursor would be a very typical symptom. If the fan is working fine and the processor heatsink is just warm, the next suspect is your harddisk. It is possible that your system is finding some "trash" on your harddisk that is causing it to crash. The "trash" I speak of could be a corrupted file or juat a program that isn't playing nice. In this case, I would run SCANDISK to see if there is an actual problem on the disk. If so, let SCANDISK try to fix the problem. If not, I would be looking for a program that is getting called everytime the problem seems to occur. To test out the "bad program" theory, consider booting into SAFE mode and see if the system crashes. If it doesn't, theproblem could be with one of the 32-bit drivers only used in NORMAL mode. If you are running Windows 98, you can use MSCONFIG to enable or disable any item in your Windows Start Up (including things called in the System Registry.)
Finally, if the above doesn't help, I would have to look towards a bad memory module and then a bad processor. That's a lot to check out. Good luck.