First thing I would do would be to remove Ubuntu and the dual boot setup. Then you probably have to repair the MBR. Then check for any missing/corrupt system files using MS system file checker (sfc /scannow) in cmd prompt. Once done and all is well, then check system for virus's and malware/spyware, defrag HDD and reboot system. Then run system like that for 3-5 days and see what happens.