I don't think your problem is RAM,
Firstly, check your CMOS settings. Which drive is the OS on? IDE, SATA etc. Make sure the system is booting from the correct HDD. If necessary, disconnect all HDDs apart from the OS HDD and see if that works. If it does, add the remaining drives back one by one until you get the same problem. If you do, then the drive you have just added is causing a confliction. Make sure you have configured it correctly. For sata, try a different cable on a diffeent port. For IDE, again, try a different cbale and make sure the Master/Slave settings are correct.
Check your drivers .. You may be able to to boot, press F6 and load from last known working configuration.
If that doesn’t work, then you can reload the SATA drivers by loading the recovery console.
Details here
http://support.microsoft.com/kb/314058
This will ask for any third party drivers as the windows files are copied. Make sure you take the repair option though
Whilst in the recovery console, perform a CHKDSK on the OS drive - CHKDSK /r /f
This may take some time to run.
It's a little vaugue but you have to start elimating in order to get to the likely cause of the problem.